I have a partial torn hamstring(right leg). a bruise appears at the gluteous fold and area behind the kneecap. what? concern?

Broken blood vessel: Bruising in both areas may be from the same source of bleeding. Will likely resolve, but compartment syndrome is a concern, ie, swelling to the point that nerves are squeezed. Emergent surgery would be required to relieve swelling. Seek care for pale skin below, numbness, or increasing deep/burning pain. Avoid aspirin or nsaids for a couple of days.