Quick question...

[Oaks]

Hi guys,
I have been playing EQ since, oddly enough 1999 on and off but never tried PvP, have decided to give it a go and apart from hideous lag at times forcing me to stop playing I'm enjoying the fear of being attacked by random folks..
My question:
Is it acceptable to attack someone while they are engaged in combat with a creature?

I ask because it seems common place and I need some clarity....don't care either way just want to know whats normal.
Thanks

Oaks, pitiful Woodelf Ranger.