Battle Rating

Battle Rating (BR) is an estimation of the power level of a champion, team, boss, player or guild. It is a rough advisory of whether you should take on an enemy or not. Factors that contribute toward BR include level, ascension status and gear.
BR isn't the be-all-end-all metric. It doesn't take into account elemental advantage, skill counters and team synergy.
==The BR bug==
There is a known visual bug where the BR of enemies are shown as much lower than they actually are. This bug appears in both Arena and Guild Wars.
left|400pxMax level enemy team (right) with impossibly low BR.	
The same enemy encountered the next day with no visual bug.