Supposedly back in juniors, Cainer was a big fighter. According to Drop Your Gloves.com, he led the Cowichan Valley Capitals with six fights during the 2006-2007 season. Below are some fights from that season (he's #20 in the dark uniform).
You can also check out his "Career Fight Card" on the site, which covers all of his fights from three years of juniors. Maybe Luke's new nickname can be Luke "Pain" Cain?
P.S. Cainer was second on the team in goals (40), assists (45), and points (85) in 2006-2007.