A substitute fielder fields for a player; a concussion replacement becomes a player.

The rules and versions used here

The general baseline is the MCC Laws of Cricket 2017 Code, 3rd Edition 2022, in force on 26 August 2026: principally Laws 1, 24 and 25 and Appendix A.8. The international variation is the ICC World Test Championship 2025–2027 Playing Conditions, effective June 2025, with the standard men's ODI and T20I conditions effective July 2025 used where their timing differs.

MCC has published a 4th Edition for 2026, but MCC says it does not take effect until 1 October 2026. This page therefore does not present that future edition as the current Law. A national board, league, tournament or age-grade competition may appoint different conditions; those conditions control that match.

Substitute and replacement are not interchangeable

MCC Appendix A.8 defines a Substitute as someone who takes a fielder's place on the field without replacing that player on the list of nominated players. The substitute's activities are limited to fielding.

A Replacement takes a nominated player's place and becomes a nominated player. ICC's Concussion Replacement is this second kind: after approval, it can bat, bowl and field as a player, subject to the Match Referee's conditions. Calling either person “the twelfth man” hides the distinction that decides what the person may do.

ICC also controls the ordinary substitute list. The WTC 2025–2027 conditions allow each captain to nominate a maximum of six substitute fielders before the toss; the standard men's ODI and T20I conditions allow four. Only those nominated may ordinarily act as substitute fielders, although the ICC Match Referee may allow a later addition in exceptional circumstances.

The umpires must accept the reason

MCC Law 24.1.1 requires the umpires to allow a substitute when they are satisfied that a fielder was injured or became ill during the match, or that there is another “wholly acceptable” reason. In all other circumstances, the Law says a substitute is not allowed.

The first route therefore requires the injury or illness to have occurred during the match. A pre-existing condition does not automatically satisfy it, although the umpires may still decide that the facts amount to another wholly acceptable reason. The provision is not a general licence for tactical rotations, rest breaks or an absence arranged solely to deploy a stronger specialist fielder.

A lawful substitute can complete a fielding dismissal

Because MCC Appendix A.7 includes a legitimate substitute within the definition of a fielder, the substitute may stop and throw the ball, take a fair catch and break the wicket in a run-out attempt. The dismissal is not invalid merely because the fielder is a substitute.

Law 24.1.2 draws the limits: the substitute may not bowl or act as captain and may keep wicket only with the umpires' consent. There is a narrow conduct exception under Law 42.7.1: when a wicket-keeper has committed a Level 3 or Level 4 offence, only a nominated player may take over as wicket-keeper even if another fielder is injured or ill.

Permission and Penalty time are separate tests

Going briefly beyond the boundary while carrying out fielding duties does not count as leaving. Otherwise, if a fielder misses the start of play, joins later or leaves during play, an umpire must be told the reason. The player may not return during a session without umpire consent; Law 24.2.2 says that consent is to be given as soon as practicable.

Permission to return does not necessarily make the player immediately eligible to bowl or bat. The player must separately satisfy the applicable Penalty-time rule. The substitute's departure and the nominated player's return restore the normal fielding eleven; the substitute has never acquired the original player's batting or bowling rights.

The current Laws use a 90-minute maximum

Under MCC Law 24.2, playing time spent absent is added to any unserved Penalty time, capped at 90 minutes. The player may not bowl until all of it has been served during later playing time—by being back on the field or while the player's side is batting. Unserved time carries into later innings and days. An unscheduled stoppage can count only under the notification-and-availability conditions in Law 24.2.6.

Law 25.3 also matters when the side bats: a player carrying unserved Penalty time may not begin an innings or act as a runner until it is served, but may bat once the side has lost five wickets. This is why Penalty time is not merely a restriction on bowlers.

International formats change the threshold and cap

Current ICC conditions do not simply reproduce MCC's 90-minute rule. In the WTC 2025–2027 and standard men's ODI conditions, restrictions begin if the absence is longer than eight minutes and unexpired Penalty time is capped at 120 minutes. In the standard men's T20I conditions effective July 2025, the same longer-than-eight-minutes trigger applies but the cap is 40 minutes.

Once the absence exceeds eight minutes, the full absence is used; the first eight minutes are not deducted. ICC conditions also allow the time to be served while the player's team is subsequently batting and retain the five-wickets exception for batting. This is a format-specific playing-condition variation, not the MCC baseline.

Four steps must connect the injury to the request

ICC clause 1.2.7 permits a Concussion Replacement only through this chain:

1. The player sustains a head or neck injury during play and within the defined playing area.
2. The Team Medical Representative formally diagnoses or suspects concussion after examining the player.
3. The Team Medical Representative or Team Manager submits the standard request to the ICC Match Referee, identifying the player, incident, time, medical view and proposed replacement.
4. The Match Referee approves a like-for-like replacement whose inclusion will not excessively advantage the team.

An injury at a hotel, in a dressing room interval or in a warm-up does not meet the current ICC requirement that the causative injury occur during play. A different competition can write a broader replacement rule, so its appointed conditions must be checked rather than assumed.

Tests and limited-overs matches use different wording

The WTC 2025–2027 conditions allow the request to be submitted within 36 hours of the incident. That accommodates symptoms which develop or are diagnosed later in a multi-day match, provided the qualifying head or neck injury itself occurred during play.

The men's ODI and T20I conditions effective July 2025 instead require the request as soon as possible after the incident. “Delayed concussion” does not enlarge the injury-location test: later symptoms can support a later diagnosis, but the request must still trace back to a qualifying in-play incident.

The remaining match role is the decisive comparison

The ICC Match Referee compares the role the injured player was likely to perform for the rest of the match with the proposed replacement's normal role. The test is practical, not a demand that two players have identical career statistics or identical labels.

The request normally identifies a player from the list of nominated concussion replacements submitted for the match. A player outside that list may be considered only in exceptional circumstances. If the proposed player's normal involvement would create an excessive advantage, clause 1.2.7.5 allows the Match Referee to control the identity or involvement of the replacement—for example, approving an all-rounder with a restriction that preserves the intended role balance.

The decision changes the nominated side for good

The Match Referee's decision is final and neither team has a right of appeal. Once approved, the injured player may take no further part in that match, even if a later assessment improves the medical picture. The replacement joins the nominated side and may take a full part subject to any imposed restriction; both players count as having played for records and statistics.

Current ICC clause 1.2.7.5 also says the replacement inherits all warnings, Penalty time and suspensions imposed on the replaced player. This prevents the replacement process from wiping out an existing match restriction.

The current WTC conditions override an older guidance note

The ICC playing-conditions hub still links a short “Concussion Replacement Guidance Note” containing older statements that a replacement need not be pre-nominated and does not inherit Penalty time or warnings. Those statements conflict with clauses 1.2.7.1.3.4 and 1.2.7.5 and Appendix A.8.2 of the WTC 2025–2027 conditions effective June 2025.

For a current WTC match, the dated 2025–2027 playing conditions are the controlling document: use the submitted list unless exceptional circumstances apply, and carry inherited warnings, Penalty time and suspensions into the replacement. The legacy note remains useful background only where it does not conflict with the current conditions.

A substitute catches the ball

Situation: under the MCC 2022 Laws, a fielder strains a calf during play. The umpires accept the injury and allow a substitute, who later takes a fair catch.

Ruling: the catch can dismiss the striker. The substitute is a lawful fielder for that delivery. The substitute still may not bowl, bat or captain, and the injured nominated player's eventual bowling or batting eligibility depends on return permission and Penalty time.

Nine minutes off means nine minutes, not one

Situation: in an ICC men's T20I under the July 2025 conditions, a player leaves because of an internal injury and is absent for nine minutes. No other exemption applies.

Ruling: the longer-than-eight-minutes trigger is crossed, so all nine minutes become Penalty time. The rule does not subtract an eight-minute allowance. The player must serve nine minutes before bowling; if the absence eventually reaches 50 minutes, the T20I cap limits unexpired Penalty time to 40 minutes.

A delayed Test diagnosis can still qualify

Situation: in a WTC 2025–2027 Test, a batter is struck on the helmet during play, initially continues, and develops symptoms later that day. The Team Medical Representative formally suspects concussion and the team submits a compliant request within 36 hours.

Ruling: a Concussion Replacement may be approved. The decisive facts are the qualifying in-play head injury, medical determination, timely request and acceptable like-for-like player—not whether symptoms were immediate.

An unapproved return produces five Penalty runs

Situation: under MCC Law 24.4, an absent nominated player comes back during a session without permission and fields the live ball.

Ruling: the ball becomes dead immediately; any applicable No ball or Wide is signalled; five Penalty runs go to the batting side; completed runs and a run in progress where the batters had crossed are scored; and the ball does not count in the over. The officials also make the notifications and post-match report required by Law 24.4.

How to analyse a substitution question

1. Name the appointed rules. Start with MCC Law 24, then identify any national, league or tournament variation.
2. Classify the person. Is this an ordinary substitute fielder or a replacement who joins the nominated side?
3. Test the trigger. For an ordinary substitute, did the umpires accept the reason? For ICC concussion, did an in-play head or neck injury lead to the required medical determination?
4. Check authority. Umpires allow the ordinary substitute and control returns; the ICC Match Referee decides a Concussion Replacement Request.
5. Track participation limits. Separate permission to field from eligibility to bowl or bat, and calculate Penalty time under the correct format.
6. Fix the final status. An ordinary substitute does not replace the nominated player; an approved concussion replacement does, and the removed player cannot return.

Five claims that are too broad

• “A substitute cannot take a wicket.” A lawful substitute may take a catch or participate in a run out; the restriction is on bowling, captaincy and unapproved wicket-keeping.
• “Eight minutes is free in every match.” It is an ICC trigger in the named current conditions, not the MCC 2022 baseline, and a longer absence counts in full.
• “Any injury allows a full replacement.” Ordinary injury normally allows only a fielder; full injury replacements exist only where appointed competition rules create them.
• “Like for like means the same player type on paper.” ICC asks what role remained in this match and whether the replacement creates excessive advantage.
• “The concussed player can return if cleared later.” Not after the ICC Match Referee approves the replacement for that match.

Governing-body sources and effective versions

• Marylebone Cricket Club — Laws of Cricket 2017 Code, 3rd Edition 2022, Law 24: Fielder's absence; Substitutes
• Marylebone Cricket Club — Laws of Cricket 2017 Code, 3rd Edition 2022, Law 25.1 and 25.3: eligibility and Penalty time
• Marylebone Cricket Club — Laws of Cricket 2017 Code, 3rd Edition 2022, Appendix A.7–A.8: fielders, substitutes and replacements
• Marylebone Cricket Club — Laws of Cricket editions and official downloads
• Marylebone Cricket Club — notice that the 2017 Code, 4th Edition 2026 takes effect on 1 October 2026
• International Cricket Council — World Test Championship 2025–2027 Playing Conditions, effective June 2025, clauses 1.2.1–1.2.7, 24–25 and Appendix A.8.2
• International Cricket Council — Men's ODI Playing Conditions, effective July 2025, clauses 1.2.1–1.2.7 and 24–25
• International Cricket Council — Men's T20I Playing Conditions, effective July 2025, clauses 1.2.1–1.2.7 and 24–25
• International Cricket Council — current Playing Conditions index
• International Cricket Council — legacy World Test Championship Concussion Replacement Guidance Note (superseded where it conflicts with the June 2025 conditions)

Checked on 26 August 2026 against the current MCC 2022 Law, MCC's next edition announced for 1 October 2026, the ICC index and the named ICC conditions. The ICC hub's legacy concussion guidance conflicts with current WTC clauses on pre-designation and inherited restrictions; this page follows the later, competition-specific WTC 2025–2027 conditions. Domestic, franchise, bilateral, junior and local conditions may supplement or replace this baseline.