It's the referee's or coach's responsibility to monitor safe play and fouls, but, in general, the intent is to go for the ball, not the player. You can't kick, trip, jump at, charge, strike, push, or hold an opponent. If a foul does occur, the team who was fouled gets a free, direct kick at the location of the foul.
Soccer is a team sport that encourages cooperation and the use of team-work for an intended goal of scoring goals. It is a game of two 45 minute halves that involves kicking, dribbling, and running. Soccer is a game in which all but one player (goalie) cannot use their hands to advance the ball.