Help! How do I stick with the punishment for my son or should I?

Ok - I (we) told my son he could not play football this next year if he had any F's in school. At the time he was not putting any effort into school & had 3 F's. Now, the year is over just took his finals & got one F in Geometry. He brought all others up to C's & B's and even one A. Now, he just called me all upset because he found out his final grade is 62%, an F in Geometry. I watched him do his work & watched & helped him study for his final. Now, I don't know what to do?? He has played football for 8 yrs. He will be a Jr. in high school, so this is first year on varsity team. He is really good, he loves football! That is his pion. (& we love to watch him), also I am on the board for the school sports fundraising. So, would you, should I stick to my (our) punishment? Would it be a bad example to let him play anyway? Before, he wasn't making an effort, but lately, he did show improvement & try. This is the hardest thing I've to do yet with him.