It's more a push than a pull. Your foot, during MaxV sprinting usually lands right under or slightly in front of your COM. When it lands here (as it should) your legs push your body upwards propelling it forwards. That is the reason why dorsiflexion of the foot is sometimes emphasized. When your toes are pointing upward upon landing, they are able to help generate more power through the stride to help push you forward.
When you overstride, your foot lands in front of your COM and your feet and subsequently your entire legs are forced to pull you forward to keep you going down the track. This foot placement results in a braking action and usually when you overstride your foot is plantar flexed and so you get minimal power output in each stride.
That's what I've learned so far….maybe someone like Mike, JJ or Phoenix can clarify