A baseball player is about to throw a baseball.
A baseball playing is throwing a ball
About to throw does not necessarily imply throwing a ball.
exists p1 s1 x1 x2.(Topic(s1,p1) & Actor(s1,x1) & a_about(s1) & exists e1 x3.(Theme(e1,x3) & Actor(e1,x1) & v_throw(e1) & n_baseball(x3)) & n_player(x1) & of(x1,x2) & n_baseball(x2))
exists e1 x1 x2 x3.(Theme(e1,x3) & Actor(e1,x1) & v_throw(e1) & n_ball(x3) & n_playing(x1) & of(x1,x2) & n_baseball(x2))