A bucking bronco causes a rodeo rider to lose his grip.
The man is riding a bull.
One cannot lose his grip and be still riding a bull at the same time.
exists e1 e2 p1 x1 x2 x3 x4.(Topic(e2,p1) & Recipient(e2,x2) & Actor(e2,x1) & v_cause(e2) & exists e3.(Theme(e3,x4) & Actor(e3,x2) & v_lose(e3)) & n_grip(x4) & of(x4,x1) & n_male(x1) & n_rider(x2) & of(x2,x3) & n_rodeo(x3) & n_bronco(x1) & Actor(e1,x1) & v_buck(e1))
exists e1 x1 x2.(n_man(x1) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_bull(x2))