A man grinds down a rail while on a skateboard.
The man is in a competition.
A man grinding on a skateboard does not have to be in a competition.
exists e1 s1 x1 x2 x3.(on(e1,x3) & n_skateboard(x3) & r_while(e1) & a_down(s1) & Manner(e1,s1) & Theme(e1,x2) & Actor(e1,x1) & v_grind(e1) & n_rail(x2) & n_man(x1))
exists p1 x1.(n_man(x1) & exists x2.(in(x1,x2) & n_competition(x2)))