Half an hour before the start of play, the two captains convene and exchange team selection sheets. This lists the composition of each side, which cannot be changed for the duration of the match, other than in the case of a concussion substitute. Then, with the supervision of the umpires, a coin is tossed to determine which captain will have the right to choose whether to bat or field. The decision is of great tactical importance, and the captain will have considered many variables before arriving at their decision. Because of the different natures of the games, it is considerably more common to choose to bat second in one-day cricket than it is in Test cricket due to batting conditions being difficult in 4th Innings.