The Physics Behind The Spider Scene: Home Alone 1
In case you've forgotten the scene...

What we can assume...
What we can take from this scene is how when Marv hits Harry over the chest, work is being done. In physics, we know that wok is equal to FdCosØ, as well as Ekfinal-Ekinitial, where Eg=mgh = (1)(9.8)(2) = 19.6 joules and that the bar comes at rest 0.03m into Harry's chest. We can also assume that the forces are in the same direction and angle so that Cos180 = -1.

So we can calculate...
Work = Ekfinal-Ekinitial
   -Fd = 0 - 19.6
-F(0.03)/-0.03 = -19.6/-0.03
      F = 653.3N in magnitude