to break down what gambling actually is you need to start with the concept of initiative.
initiative = Having a timing advantage.
For example, riposting gives you initiative - you can have a maul and them a dagger, but the maul riposte will land first compared to the dagger, as you have the initiative due to the riposte. Initiative is really important in Mordhau, as we have first hit flinch in most situations; if you hit first you're protected, and then enemy goes into flinch and you can combo, and keep the initiative etc.
Gambling is the act of attacking without initiative. If you have a timing advantage (initiative) and are mid attack while the other person is just winding an attack up, you will hit them first every time if you just commit to the attack. Why gambling is annoying is because, well, it's a gamble that revolves around someone doing an attack out-of-turn which shouldn't work, but if you happen to feint or do a big drag or something, they hit you. They're just rolling the dice and hoping that you forfeit your initiative mid-swing, and it's illogical but can definitely catch people off-guard, so it can be effective at times.
Gambling isn't:
- Reading a feint and trying to punish it
- Going for a chamber attempt
- "stealing" initiative if the other person hesitates
- spamming attacks (can be a gamble but normally the timing is off)
- using footwork/range to cause misses and punishing whiffs
The More You Know™