it's not just YF parents, it's parents in all sports...the best thing for parents to do is STFU and enjoy the games and support your kid...harder to do than it sounds though.
My son must be the same age as yours (just turned 13 and in the 8th grade), he's a very good athlete, been an All Star in baseball and basketball every year since he was about 9...anyway, he's smaller than other kids his age, (even though I'm 6'4") and has yet to hit his growth spurt, but he's extremely quick, tough and athletic...anyway, he's been playing football for the last 3 years and it's been very frustrating for him. He's excelled at every sported he's tried (lucky bastard)..He wasn't even sure he wanted to play football this year since his role was reduced last year in favor of an older, bigger kid (they had about equal abilities). I was really PO'ed last year about his playing time, but I kept my mouth shut and said nothing, but I was tempted. I wasn't going to encourage him to play this year because I thought the coach "wasn't being fair" to him. The day of the first practice this year, he decided to try again, and I supported him...reluctantly. He started out low on the depth chart but has now become the starting WR, KR and PR...he may still be a "smurf", but he's a tough little bastard who has earned his postion through hard work and determination. The bottom line is he made it impossible for the coaches to keep him off the field, he makes the plays. Parents need to let the kids earn the playing time and keep away from coaches, they are not doing thier kids any favors by butting in...most coaches are very fair people who volunteer a tremendous amount of time and effort to coach and teach all the kids, sadly, this is often overlooked by parents who can't get past "playing time"...kids will get more out of it in knowing they are the one's that are responsible for their own success, not because mom or dad bullied the coaches...