Which player can be tripped legally during a game?

In a football game, the runner, who is typically a ball carrier attempting to advance the ball, can be tripped legally by a defensive player while engaging in the play. This is a key aspect of the game's rules regarding physical contact and defensive maneuvers.

When a player has possession of the ball and is running, defensive players are permitted to try to stop them using various legal methods. Tripping, as a tactic to thwart the runner's progress, is allowed as long as it is executed within the rules, such as avoiding dangerous plays or using excessive force.

The other players mentioned have specific protections under the rules. The quarterback, punter, and kicker are often in vulnerable positions while executing plays and generally have protections against certain types of contact. The rules seek to minimize the risk of injury to these players, especially as they may not be in a position to defend themselves adequately during their respective actions. Therefore, tripping these players is considered illegal and would result in a penalty. The runner stands out as the only player among the given choices who can legally be tripped during the course of play.