A man in a white helmet crouches while he skateboards.
A man wears his skateboard as a helmet.
One would not be on skateboards and wear it as a helmet at the same time.
(x)
exists e1 x1 x2 x3.(Theme(e1,x2) & Actor(e1,x1) & v_wear(e1) & as(x2,x3) & n_helmet(x3) & n_skateboard(x2) & of(x2,x1) & n_male(x1) & n_man(x1))