The football players are working on stretching their legs.
The football player hurt his leg.
Football players is plural; football player is singular.
exists e1 e2 x1 x2 x3 x4.(n_leg(x4) & of(x4,x1) & n_thing(x1) & n_player(x1) & of(x1,x2) & n_football(x2) & on(e1,e2) & Theme(e2,x4) & Actor(e2,x3) & v_stretch(e2) & Actor(e1,x1) & v_work(e1))
exists e1 x1 x2 x3.(n_leg(x3) & of(x3,x1) & n_male(x1) & n_player(x1) & of(x1,x2) & n_football(x2) & Theme(e1,x3) & Actor(e1,x1) & v_hurt(e1))