We present and defend a view labeled “practiceism” which provides a solution to the incompatibility problems. The classic incompatibility problem is inconsistency of:1. Someone who intentionally violates the rules of a game is not playing the game. 2. In many cases, players intentionally violate the rules as part of playing the game (e.g. fouling to stop the clock in basketball). The problem has a normative counterpart:1’. In normal cases, it is wrong for a player to intentionally violate the rules of the game. 2’. In many normal cases, it is not wrong for a player to intentionally violate the rules of the game (e.g. fouling to stop the clock in basketball). According to both formalism and informalism, the rules of the game include the formal rules of the game. Both traditional positions avoid the incompatibility problems by rejecting 1 and 1'. Practiceism rejects 2 and 2’: it maintains that the rules are the rules manifested in playing the game, not the formal rules. Practiceism presents two theses: (a) the real rules of the game are the rules players follow: the practice determines the rules, and not vice versa. (b) the (first order) rules of a game determine what is legitimate within the game.