Throw-ins occur when the ball goes out of bounds. From wiki: “A throw-in is a method of restarting play in a game of football when the ball has exited the side of the field of play”.

bet365.com is one of those online sports betting apps where you can actually bet on the number of throw-ins that will take place in a match.
You can wager on the total amount of throw-ins in an over/under type wager, of which team will get the most throw-ins.
To make a bet on total throw-ins, you must really have a hunch of what’s going to happen over the course of the game.
To be honest, this is one I would stay away from at all costs. But if you have a feeling, go with it.