Football players engaged in a tackle.
Football players are on a football field.
Not all football players engaged in a tackle are on a football field.
exists e1 e2 x1 x2 x3 x4.(Actor(e2,x1) & v_tackle(e2) & in(e1,x4) & n_a(x4) & Theme(e1,x3) & v_engage(e1) & (x1 = x3) & n_player(x1) & of(x1,x2) & n_football(x2))
exists p1 x1 x2.(exists x3 x4.(on(x1,x3) & n_field(x3) & of(x3,x4) & n_football(x4)) & n_player(x1) & of(x1,x2) & n_football(x2))