Laws of Cricket 1947 Code - Law 1
A match is played between two sides of eleven players each, unless otherwise agreed. Each side shall play under a Captain who before the toss for innings shall nominate his players who may not thereafter be changed without the consent of the opposing Captain.
Notes on Law 1
1. If a captain is not available at any time, a deputy must act for him to deal promptly with points arising from this and other Laws.
2. A side should not field with more than eleven players.
Reproduction of the Laws of Cricket is by kind permission of Marylebone Cricket Club