If they were going to score a try with certainty and a defender came in with an intentional swinging arm and broke the potential try scorer's jaw, could it not be both a penalty try and a sin bin or send off?
Yes.
Modern day interpretations and wording confuse things, but the way the rule has always been is…
Foul Play = holding back, holding down, offside, etc. Also - getting involved in a fight was included in foul play (you can be sent for 10 mins to calm down) but punching/striking was not.
Misconduct = everything else (high tackles, etc.)
Penalty tries exclusively relate to foul play (excluding fighting. If there is misconduct that can be punished separately, via an 8 point try, penalty, sin bin, or send off.
The average punter misunderstands the rules, thinking that a high tackle or late hit is “foul play” when it is actually considered “misconduct”. In the past, it was never possible for the sin bin to be used for misconduct, but the NRL changed this in 2016 to allow the sin bin for punching, and then again in 2018 to allow the sin bin for any misconduct…