A man grinding down a handrail.
A man is skateboarding.
Not everyone who grinds a handrail is skateboarding.  They could be BMX biking, for instance.
exists e1 s1 x1 x2 x3.(a_topic(x1) & a_down(s1) & Manner(e1,s1) & Theme(e1,x3) & Actor(e1,x2) & v_grind(e1) & n_handrail(x3) & (x1 = x2) & n_man(x1))
exists e1 x1.(Actor(e1,x1) & v_skateboard(e1) & n_man(x1))