Suit Dynamics

Men's suits get interesting when the pose moves out of neutral. I sketched the same speaker as he shifted back and forth between two poses during his talk. 

The jacket and pants hang fairly straight in the left pose. But as he put his hands in his pockets, new points of tension emerge. Folds radiate from the red arrows at the button and the hand. A long pipe fold on his pants leads all the way down past the knee. Because he lifted his shoulders, folds also radiated from his shoulders. 

In this illustration by Austin Briggs from the Famous Artists Course, the leaning-back figure has folds radiating from the shoulder seam, the knee, and the crotch. But the back is fairly smooth.

There's no substitute for drawing from the costumed model to learn these dynamics, which change not only with the pose, but also with the type of fabric and the construction of the garment.