A boy on a skateboard grinding down a handrail.
The kid slides down the rail on his skateboard.
Grinding a rail means simply to slide down or across something.
exists e1 s1 x1 x2 x3 x4.(a_topic(x1) & on(x1,x2) & a_down(s1) & Manner(e1,s1) & Theme(e1,x4) & Actor(e1,x3) & v_grind(e1) & n_handrail(x4) & (x2 = x3) & n_skateboard(x2) & n_boy(x1))
exists e1 s1 x1 x2 x3.(n_skateboard(x3) & of(x3,x2) & n_male(x2) & n_rail(x2) & n_kid(x1) & a_down(s1) & Manner(e1,s1) & Theme(e1,x2) & Actor(e1,x1) & v_slide(e1) & on(x2,x3))