Question

What can cause leg stiffness or tightness?

Answer 1

Lots of information here http://www.livestrong.com/article/136909-causes-leg-pain-stiffness/ Please consult a doctor if the stiffness continues.

Answer 2

If you don't stretch in properly after working out, or if your muscle gets cold it tends to contract. You can fix this by stretching it back out or by putting some heat on it.