When I see a lot of elite sprinters accelerating, my impression is they are getting their foot down as quickly as possible. I think that in order to do that you have to impart a lot of force, so you get a combination of both. The pushing comes as a side effect of getting your foot down fast, but the forwards emphasis reduces the chance of wasting time by pushing harder and longer than you need to.
Didn’t Charlie say you sprint over the track, not on it? I think he also said it should be fast, not hard. Opposite of … Something…