Reverse Gear

Hey guys,
I have a 95 grand am, quad for with a 5 speed, somtimes when I begin to put the car in reverse gear it will disengage with a snap. The shifter wont move, and i'll have to pull it out and put it back in and try again. It's been on going for a couple months now but it's definetly getting worse.
Anyone know what's goin on?

Thanks