The man in the background is watching the skateboarder complete a jump.
A man is watching his son jump with the skateboard.
That the man is watching a skateboarder does not imply any relationship, such as the skateboarder is his son.
exists e1 e2 x1 x2 x3 x4 x5.(n_skateboarder(x4) & n_background(x2) & n_man(x1) & Theme(e2,x5) & Actor(e2,x1) & v_complete(e2) & n_jump(x5) & in(x1,x2) & Theme(e1,x4) & Actor(e1,x3) & v_watch(e1) & (x2 = x3))
exists e1 e2 x1 x2 x3 x4.(n_skateboard(x4) & with(e2,x4) & Actor(e2,x1) & v_jump(e2) & Theme(e1,x3) & Actor(e1,x2) & v_watch(e1) & n_son(x3) & of(x3,x1) & n_male(x1) & (x1 = x2) & n_man(x1))