I just saw that movie “Rudy”-about the kid who wanted to play football for Notre Dame University. He struggles for years (gets admitted to ND as a conditional student)…He finally makes the tryouts and gets on the “B” team. I had to really admire this kid’s determination…he knew he wasn’t good enough to play for the A team…finally, in his junior year, he begs the coach (Ara Parsegian) to let him suit up and at least get on the field, for once in his last year!
Now, I have never played football, so I don’t know the details…but how do you stay motivated as a “B” team player? Football practices are brutal…I can’t imagine going through 2 hours of blocking practice, every other day during the season (and knowing that you will most likely never play a real game!
You really have to LOVE the sport to do this.how often does a coach send in a B team player? 
Depends on lots of stuff.
Player injuries can do it: In today’s game against UCLA, Illinois’ main quarterback Jon Beutjer was injured in the first half, and the rest of the game was played by redshirt-Freshman QB Brad Bower.
Blowouts can do it: Western Illinois beat Cheyney State 98-7. They were leading 70-0 at the end of the first half. I don’t know for certain, but I imagine there were some second-string players playing, maybe on both sides of the ball.
Mostly, though, a player on the B team will just hope he gets good enough next year to be a starter or a sub.
In the case of “Rudy”, I think “B” was equivalent to what is usually called the “scout team”.
College teams usually have a group of players whose job it is to emulate the upcoming opponent. They rarely see action in a game all year and don’t make road trips.
These are quite often the people who will end up coaching your kids in middle school. To play on a college scout team, you have to truly love the game and have given up on the idea of playing in the NFL- but it doesn’t mean you can’t make a career out of football.
Even a B team guy gets plenty of tail.