I'm currently on my 2nd round of DC Training, and I've been strictly lifting for about 1.5 years now without any other activity more or less (the occasional football game). 2 weeks ago we set up a quick pickup game of football, and I first pulled my right hammy, then about 20 mins later after continuing to play, pulled my left (although the left pulled much worse). Since then, whenever I try exploding in any sport (played basketball yesterday, but not a serious game), I keep pulling my hammys. Also, since the first pull 2 weeks ago, I haven't been able to DL properly and couldn't even leg curl 25lbs with my left leg, it just felt like too much weight.
If the issue here is stretching (which I would think is the obvious answer), then how much stretching is really necessary here? I'm very bad with stretching. I don't stretch during, before or after workouts (although I lift very light to begin for 10 reps and make my way up to the heavier weight). Is this the culprit for these overly tight hammys?
How do I get my hammys back to normal? And if its stretching, please recommend some stretches and how long they should be held for.