I agree with working on flexibility. Strong abs and core will help as well, but you gotta get your flexibility going. Try dynamic warm ups, hurdle drills, and hip mobility on the ground drills which Im sure are somewhere on this site.
Get with a college athlete for the dynamic warm up stuff for ideas if you dont know any, track athletes for the hip mobility and hurdle drills, or Im trying to think of books that have these drills in them...Renegade Training for Football by Coach Davies has explanations and pictures of tons of flexibility stuff/hurdles, so does Complete Conditioning For Football by Michael Arthur and Bryan Bailey (Nebraska S&C stuff).
Working front squats will force you to stay back on your heels and keep your core tight, overhead squats just with the bar in a snatch grip, and I like heavy RDLs to forcing the hips back and keeping a power position with the back arched stretching your hammies really good. I think calf flexibility comes into play with people who have hard time going deep as well. If you are new to squating try pointing your toes out slightly if you are not already.
After you train, do tons of static stretching. Dynamic warm ups before, static after.
Hope this helps