A substitute fielder is not the same as a concussion replacement.

What a substitute fielder is

A substitute fielder is someone allowed by the umpires to field for a nominated player who is off the field. Under the Laws, the umpires allow one when they are satisfied that a fielder has been injured or become ill during the match, or when there is another wholly acceptable reason for the absence.

The substitute does not replace the player in the batting order or bowling attack. The original player remains the nominated player and may return, subject to the absence and penalty-time rules that apply in that match.

A substitute can field, but not bowl

An ordinary substitute fielder can take part as a fielder. That means the substitute can stop the ball, take a catch, complete a run out, and otherwise field like a member of the fielding side for that delivery.

The limits are important: the substitute cannot bowl and cannot act as captain. A substitute may act as wicket-keeper only if the umpires consent. That keeps the rule from becoming a tactical way to bring in a specialist bowler or captain while still allowing the match to continue with eleven fielders.

Umpires decide whether the reason is acceptable

The fielding side does not get an automatic substitute just because it asks for one. The umpires must be told why the player is absent, and they decide whether the reason fits the Law or the playing conditions.

Injury and illness during the match are the clearest reasons. Short absences for practical needs can also be acceptable, but using substitute fielders as a planned rotation system is not the purpose of the Law. If the reason is not acceptable, the substitute should not be allowed.

Leaving the field can affect bowling or batting

A player who leaves the field or fails to take the field generally needs umpire consent before returning during a session. If the player has been absent long enough, they may also have penalty time to serve before bowling again, and in some matches before batting.

The exact timing rules can differ between the MCC Laws and competition playing conditions. The practical point is the same: a bowler cannot always leave the field, use a substitute, return immediately, and bowl straight away. Officials track the absence and apply the relevant penalty-time rules.

Returning without permission can be penalised

If a player returns to the field without the required permission and then contacts the ball while it is in play, the umpires can call Dead ball and award penalty runs to the batting side. A no-ball or wide signal can still be recorded if it applied to the delivery.

This is why substitutes and returning players are managed through the umpires rather than informally from the boundary. The scorer, the other umpire, the captains, and the batters may all need to be told what has happened.

Concussion replacements are different

A concussion replacement is a full replacement player used under competition playing conditions, not an ordinary Law 24 substitute fielder. In ICC playing conditions, the rule applies when a player sustains a concussion or suspected concussion from a head or neck injury during the match, in the playing area, and the team medical representative formally diagnoses or suspects concussion.

The request is made to the match referee on the required form. It identifies the injured player, the incident and time, the medical view, and the proposed replacement. The replaced player takes no further part in the match once the concussion replacement is approved.

The replacement must not give an excessive advantage

The central test is like-for-like replacement. The match referee considers the likely role the concussed player would have played for the rest of the match and the normal role of the proposed replacement.

If the proposed player would give the team too much advantage, the match referee can refuse the request or impose conditions on what the replacement may do. For example, a competition official may restrict a replacement's involvement if an all-rounder is being used to replace a specialist batter.

Modern playing conditions can require pre-nominated replacements

At ICC level, captains nominate the playing eleven and a limited number of substitute fielders before the toss. Recent ICC playing conditions also refer to nominated concussion replacements, with exceptional circumstances allowing the match referee to consider someone outside that list.

Domestic competitions can write their own version of the process. The safe general rule is to check the playing conditions for the match, because the Laws provide the ordinary substitute fielder framework while concussion replacements are competition rules layered on top.

How officials sort the incident

1. Identify whether this is an ordinary absence or a concussion replacement request.
2. If it is an ordinary absence, ask whether the umpires accept the reason for a substitute fielder.
3. Confirm what the substitute is allowed to do: field, possibly keep wicket with consent, but not bowl or captain.
4. Track whether the original player needs permission to return and whether any penalty time affects bowling or batting.
5. If it is concussion, apply the competition's medical diagnosis, request, approval, and like-for-like replacement process.

Misunderstandings to avoid

• "A substitute fielder is a twelfth player" is too broad. The substitute can field, but does not become a full batter or bowler.
• "A substitute cannot make a dismissal" is wrong. A lawful substitute fielder can take catches and complete fielding dismissals.
• "Concussion substitutes work for any injury" is wrong. They are tied to concussion or suspected concussion under the relevant playing conditions.
• "Like-for-like means identical skill" is too strict. Officials compare roles and advantage for the rest of the match, not whether the players are exact copies.
• "A player can step back on whenever they want" is wrong. Returning to the field is controlled by the umpires, and penalty time can affect later participation.

Source material

• MCC Law 24: Fielders' absence; Substitutes
• ICC Playing Conditions
• ICC Men's Test Match Playing Conditions - June 2025