What exactly is a malicious miner doing when bamboozling a random outcome for a game by throwing away a block?

I’m a noob with dev.

Please explain this to me.

I keep reading that it costs money to throw away a block in an attempt to bamboozle a random outcome for a game contract, assuming the random number was based on seemingly random information in a future block.

So if the potential winnings are lower than the cost of cheating it wouldn’t be worth it to the malicious actor.

For instance - how can I can I calculate or understand the cost of throwing away a block?

I would appreciate any information on this.