When must I allow a substitute fielder or a runner?

Q: When must I allow a substitute fielder or a runner?

Under the Laws of Cricket (2017 Code, 4th Edition 2026): Substitute fielder (Law 24.1) You must allow one if satisfied a fielder has been injured or become ill and this occurred during the match, or for any other wholly acceptable reason. In all other circumstances a substitute is not allowed. A substitute may not bowl or act as captain. They may keep wicket only with the umpires' consent. Runner (Law 25.5) You must allow a runner if satisfied the batter has sustained an injury that affects their ability to run and that this occurred during the match, or for any other wholly acceptable reason. Otherwise no runner is allowed. The runner must be a member of the batting side and, if possible, have already completed their innings. They can be changed only with the umpires' consent, must wear external protective equipment equivalent to the injured batter's, and must carry a bat. Fielder who leaves the field (Law 24.2) A fielder who is absent must have the reason given to an umpire. They cannot return during a session without an umpire's consent, which the umpire gives as soon as practicable. They cannot bowl until they have served Penalty time back on the field (the time they were off, up to a maximum of 90 minutes). Penalty time is not incurred if the player left because of an external blow during the match, or for other wholly acceptable reasons in the umpires' opinion, which do not include illness or internal injury (Law 24.3).

Question

Accepted Answer

Under the Laws of Cricket (2017 Code, 4th Edition 2026):

Substitute fielder (Law 24.1)

You must allow one if satisfied a fielder has been injured or become ill and this occurred during the match, or for any other wholly acceptable reason. In all other circumstances a substitute is not allowed.
A substitute may not bowl or act as captain. They may keep wicket only with the umpires' consent.

Runner (Law 25.5)

You must allow a runner if satisfied the batter has sustained an injury that affects their ability to run and that this occurred during the match, or for any other wholly acceptable reason. Otherwise no runner is allowed.
The runner must be a member of the batting side and, if possible, have already completed their innings. They can be changed only with the umpires' consent, must wear external protective equipment equivalent to the injured batter's, and must carry a bat.

Fielder who leaves the field (Law 24.2)

A fielder who is absent must have the reason given to an umpire. They cannot return during a session without an umpire's consent, which the umpire gives as soon as practicable.
They cannot bowl until they have served Penalty time back on the field (the time they were off, up to a maximum of 90 minutes). Penalty time is not incurred if the player left because of an external blow during the match, or for other wholly acceptable reasons in the umpires' opinion, which do not include illness or internal injury (Law 24.3).