Blind Football

Who would have thought there's actually blind football！ In fact, the proper term should be Football 5-a-Side or 7-a-side. The difference between the two is number of players in a team. One of the challenge in watching this game is that we had to restrain ourselves from cheering every time our favorite team score. The reason? As you may have already guessed - the players can't hear the ball. The part I couldn't figure out is how do they differentiate team players and opponents?