just report them, and then do this
1. type "report afkers at [boat/farm/FR]"
2. highlight text and hit ctrl C
3. copy paste 6 times into bg chat, and continue copy pasting 6 times every 15 seconds until those people are kicked from the BG.
i can tell you from extensive experience that this usually works. i can also tell you from extensive experience that just saying "report afkers" doesn't work.
if people take offense to your use of bg chat to accomplish something incredibly helpful, point out to them how stupid it is to put 15 minutes of effort into trying win a 6v10 BG while being too lazy to spend 2 seconds clicking on a clump of dots in order to add 3 or 4 players to your team. spamming bg chat to get afkers out is by FAR the best possible use of bg chat when you're losing due to bots. no amount of strategy or coordination is going to save you when you're badly outnumbered. it's absolutely mind-blowing that people try so hard to win, attempt so hard to strategize and coordinate in bg chat, yell with such rage at everyone for allegedly playing badly, all while being too stupid and lazy to take the single best and most efficient action they can take to win a bg.