When a teammate must leave mid-game, a calm process protects the player, the opponents and the result. The general World Bowls rule is specific, and domestic rules may add detail.
Start with the 10-minute rule
Law 32.1 says a player must not delay play by leaving without the opponent’s agreement, and that agreement covers no more than 10 minutes. If a team or side player cannot return within 10 minutes because of illness or another reasonable cause, the umpire or controlling body may approve a substitute.
Agree that a substitute is needed
Under law 32.3, both skips should agree that substitution is necessary. If they cannot, the umpire or controlling body decides. The controlling body also decides whether the proposed substitute is eligible.
A substitute cannot skip
Law 32.4 places the substitute in a position other than skip. Other team members may rearrange their positions as needed. Record who joined and when, especially if the match uses a paper or digital card.
Singles and unavailable substitutes
If a singles player cannot return within the permitted time, they forfeit. If a team has no eligible substitute, law 32.6 sets different consequences for a team game and a side game. Ask the official before continuing short-handed.
Source: World Bowls Laws of the Sport, law 32. Check your national regulations and event conditions before a competitive game.
Check the event’s domestic regulations before the first end, not after a teammate leaves.
For a shared view of close heads, try WGTS for iPhone or WGTS for Android. Use the official measuring procedure whenever your competition requires it.