Push-ups, planks, pull-ups. Also, easy hamstring, glute and hip flexor exercises with ankle weights--no pain, but weak in left hamstring; eccentric calf raises on stairs; lying-on-side leg lifts.
Note: I used ice a few times for first 48 hours after the injury, and then began using heat. A few days after injury, I began doing some cross fiber massage on the left hamstring. It very slowly gets a little better, but still pain and stiffness, and when I first begin massage it hurts to the touch, getting better after a few minutes.