"Backstabber" would probably mean that, whether intentionally or by accident as he gets carried away with hitting everything in range, he may hit someone on his own side. This would probably involve either removing the protection currently in place by which you can't harm anyone in your own team, or put him into his own AI group. The former will probably play merry havoc with combat balance, while the latter will probably play merry havoc with AI relations. Either way, expect this character to have a life span of about 10 seconds if the trait activates and he does hit one of your other officers. (Or, if you can see his traits at the time of hiring, no sane captain will ever hire this character. )