Is there a reason my leg muscles continue to grow tighter even if i'm not putting pressure on it?

Yes : Usually turning your foot/ toes toward you with your hand - gives relief to the spasms.

Passive contraction: This condition is usually referred to as muscle spasm. Muscle spasm is a spontaneous muscle contraction: as the muscle contracts, it grows tighter. When you put pressure on it, the ground reactive force causes the contraction. If you are not putting pressure, it is a spontaneous contraction, and could be due the muscle fatigue (or less often, it is from low serum potassium).