Casero is correct - one should always state intentions when entering a combat in progress, if only to alert those engaged of your presence in case they are distracted. "Hold on, reinforcements have arrived!" or somesuch variant is always good RP.
As for the rues lawyering, I trust sensible players to be able to sort OORP matters out amongst themselves in a civilized manner without having to resort to shouting. I know there are a lot of infuriating rules lawyers out there who do so in an unhelpful way, but it is always worth assuming that people are just trying to help unless obviously otherwise.
Anyhow, no great matter, just a bit of advice. Thanks.
Sir Stanley Nelson <span style="color:#000066">Charles Canning </span><span style="color:#000066"> Foreign Secretary</span>