^ Free bet on sports betting?
I did not hear bookmakers offer such kind of promotion not like a free spin on wheels or free bet on dice, they are totally different.
Maybe there is a promotion something similar to what you have asked but that is a rare case, if there is, you can find out on the games and round section or it will announce or their announcement thread but that is rare to happen. I have heard before, a free bet when you deposit on the site, but I dont think that promo has been existed until now. Most of them are not.
Nevertheless, why not have a deposit on your own and place a bet.