I have had a few young horses or older spoiled horses try this move, and yes, in a soft area, you will just have to drop the foot at the right time to let them 'fall'. I then will usually work their tails off for a while; if they think it's easier to 'fool around' then, fine...work it is. I do not ever allow a horse lean on me; I physically can't handle it. So they have to learn to behave. Start lifting the foot at short increments...if he behaves, release and praise, if not, drop it, so he 'falls', work him some, and start over.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."