I had the same problem, and stil do some times. You need to start stretching your groin every morning, and after your warm up sets.
Heres what I do and it has helped.
1.)Legs a little bit further than shoulder width and lean to one side until you feel a stretch and hold it for about a 15 count, stand up shake it out then do it to the other side.
2.) Drop to a knee like your doing lunges and lean back and push back on the upright knee. Hold for about 15 and then do it to the other one.
3.) laying on your side pull one leg to you butt and do a stander quad stretch butlean back with your upper body while pulling back on your leg...hold for 15 then do it to the other side.
*Also doing hip abduction and hip Aduction will probably help the problem too, the exercises you see all the girls doing where they open their legs like they're getting ready to take it and close them and vis versa....
Hope this helps