Continuity mistake: When Jesse and Lisa are making out on the floor you see Jesse holding Lisa's arm. When it cuts, Jesse has both his hands on Lisa's breasts. (00:50:40)
Continuity mistake: When Lisa's mother turns off the light you see two guys wearing blue shirts standing outside. When they see the light turns off they turn around. When it cuts they turn around again. (00:50:00)
Continuity mistake: When Jessie sits on the ground after being hit by the baseball you see him about to get up. Then Schneider approaches him and when it cuts you see Jessie sitting still. (00:08:50)
Answer: I think the coach's death was a play on his character being at a S&M bar. People who frequent those places are usually into bondage and being dominated. Hence being tied up, and whipped with the towel. It also fits in with the homoerotic subtext throughout the movie.