Gameplay and Rules
The challenges and actions of a sports game are those of the actual sport but with the actions of the athletes' bodies mapped onto the control devices of the game machine. Whatever the athletes try to achieve in the match, the player tries to achieve. In the coaching role, the challenges are to choose the most appropriate strategy for the moment from among those offered by the game and to manage the athletes so that they don't become overtired or injured (assuming the game implements those concepts).
The rules of a sports game are, for the most part, the rules of the sport in the real world. You might find that you need to relax these rules in some areas, particularly with respect to faults, fouls, or judgment errors that the player might make. Because the player is using a handheld device to manipulate an athlete on-screen instead of playing on the field himself, it's much more difficult to judge when his avatar is about to bump into someone, cross into a forbidden zone, and so on. A few games allow the player to set the level of computerized refereeing to forgiving or strict, depending on which way he likes to play.
You also have to decide if you want to simulate athlete mistakes that are outside the player's control. For example, in American football, penalties are called for holding, grabbing hold of another athlete instead of merely pushing him. This is an aspect of the sport that a computerized version might have difficulty simulating and could avoid entirely: The game could simply make it impossible for one athlete to hold another. However a match in which no holding penalties ever occurred would feel unrealistic. On the other hand, a match in which the player is randomly penalized for holding when he hasn't actually done anything wrong might be frustrating for some players. Allowing the player to adjust the refereeing mechanism can solve this problem. Under realistic refereeing, the game would generate penalties at random at about the same rate at which they occur in real matches. Under relaxed refereeing, the game would not generate any penalties except for those actually under the player's control.