I'll go into detail later tonight when I get more time. But for the time being, to answer your question, the most likely muscle that's tight for you is your calves. When you say you have to lean forward, do you mean that your heels come off the ground? Heels off the ground and feet turning outward are the two most common signs of tight calves.
Please post muscle imbalance corrections, especially lower body, when i squat down i have trouble keeping my shins straight and if i do i have to lean foreward