PvP casual here and need a bit of help.

How exactly does this one hit kill work? It's really annoying playing with my Paladin and then randomly getting one shotted by some SAM.

I asked in the game but I couldn't get any straight answers.

So i was told to "simply" don't attack them.

What does this mean exactly? Do I avoid SAMs at all cost or is there a time period where I can't touch them or I get one shotted?

I was also told to not touch them while they have their LB but how exactly does one know when another player (a rival) has a LB ready to go?

Helpful tips and answers will be appreciated.