Besides exertional compartment syndrome, what other things would cause gastrocnemius contracture whereby need to flex at knee to dorsiflex foot?

Achilles tightness: As you've mentioned 'exertional compartment syndrome', I'm going to guess that you: 1. have had this diagnosed and 2. have transitory symptoms. Compartment syndrome usually presents with pallor, pain, paraesthesias, 'pins and needles' sensation and pulselessness. If your calf simply feels tight, it doesn't rule out CS, but it is less likely. Chronic CS should be worked up before a muscle tear.