Is it out of line to make your child participate in sports practices? [POLL]

My son participates in Karate and seems to love it. He has missed a few practices due to illness and funerals, other than that he has attended every practice. That almost changed last night. My son got to Karate and decided that he didn't want to participate. He just wanted to sit and watch...he had no other real reason for not wanting to participate, he just wanted to watch. Our discussion soon became the highlight of the room because I had to inform that there would be punishment when we got home if he choose to sit and watch instead of join his class. Luckily my son made a good choose by joining his class and he had fun. It still made me wonder if I was pushing him to hard to do something he didn't want to do...but then, I hear my dad's voice tell me, "You don't start something without finishing it."