I recently saw this clip of a play in a Canadian football game and it made no sense to me as well as not being something that would be allowed in American (normal) football.
(Full Disclosure: I’ve NEVER watched a Canadian football game in my life except for the 11 seconds …. wait, to be honest, I watched it 3 or 4 times to try and figure out wtf I was seeing, so write me up for 44 seconds total time.)

What are they doing … ? and why did they do this on a 2nd and 18?

(Thanks to my sports freak brother, Danny) Turns out this a rule that applies to Canadian football only. I heard conflicting comments about who has to remain behind the line of scrimmage and who doesn’t but basically when you punt the ball, anyone behind the player kicking is onside (including the kicker) is eligible to recover the ball.
The ball has to cross the line of scrimmage.
This resulted in a recovered punt for a first down.

https://twitter.com/NFL_DovKleiman/status/1708248643319255247

This article attempts to explain the rule but its still confusing and shows several examples of the ‘onside’ punt play.

https://thecomeback.com/international/cfl-rules-debate-onside-punt-montreal-alouettes.html