The boy does a skateboard trick.
A boy riding a skateboard.
If someone does a skateboard trick then it is implied they are riding a skateboard.
exists e1 x1 x2 x3.(n_boy(x1) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_trick(x2) & of(x2,x3) & n_skateboard(x3))
exists e1 x1 x2 x3.(a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_ride(e1) & n_skateboard(x3) & (x1 = x2) & n_boy(x1))