He had a problem with his hamstring.
Okay....so they don't get any better, sometimes you just can't help yourself.
So, hamstring.....ham - came from the fat behind the knees, string.....referring to the several tendons.
There you have HAMSTRING
Walking, running, jumping and even stability would be difficult with an injury to the group of tendons contracted by the four muscles that make up the thighs - also know as The Quads