Even if you start with $2 and go all in every bet @ 2.00 odds, after 19 bets you will be at $1,000,000. Or if you start with $500, it takes 9 all in bets to reach $1,000,000. It is possible.
It's possible to arrive at that amount; that's it. You make those series of bets in a role going all in without losing, which is also on the second thought not possible; if it were that easy, most casinos would have been out of business for a long period of time now. I can't say it's entirely impossible to get such a reward, as strange winnings do happen, but such is hard to fine and very uncommon.
Mathematically it's possible, but it could be very hard to hit as we all know that there are games that are really unpredictable, and when you think that you will win, then suddenly there will be bad events and you might lose.
And so for that to happen, you really have a extreme luck on your side to make millions in gambling. Everything should fell into pieces for you and so one can stop you from winning that. So it's going to be based on your luck to make $50 to a million in short amount of time in sports betting.