If you lose your game in blackjack, re-enter with x2 amount.
If you step on the wrong tile, x2 increase the wager amount.
etc. It is easy.
The process is easy though the results could turn out to be horrible in the long term which is why it is a very risky strategy. I prefer Oscar's grind since it is more conservative and helps your bankroll last longer in this regard.
I just told you how you can use this.
So you are telling me that I can't apply martingale to sports betting. Watch me how I do it:
Juventus : Napoil pick draw, result: Juve wins, increase the wager amount x2
Juventus : AC milan pick draw, result: AC milan wins, increase the wager amount by x2 again
Juventus : Cagliari pick draw, result: Draw, congratz you made some profits.
See? You can apply to anything and I mean literally ANYTHING.