Goal for means ,goals made by your team on your rival teamand goal against means goals made by your rival team on your team.

goal for means scoring a goal for a particular team and goal against means scoring against that particular team ie. for the opposition.eg. there are two teams playing a match in a tournament say X and Y. if a player of team X scored a goal for X against Y that goal is termed as goal for X and in terms of team Y it is termed as goal against Y