"Team Luke" is a reference to a once bizarrely popular series that has since faded away into obscurity, never to be mentioned or referenced in more than vague ways evermore.
Nonetheless, the series made a big thing of a love triangle within it between a teenage girl with poor judgement, some really super old guy who looked young but was nonetheless super old for reals, and an age appropriate cool guy with great abs. Those who wanted her to be with the old guy were "Team Old Guy", and those who wanted her to be with the cool guy were "Team Abs".
I should probably note that it's entirely possible that there are a whole mess of factual errors in the preceding paragraph and I have never actually read Twilight--er, that which must not be named. "Team Edward" and "Team Jacob" were a thing, however, which sort of baffles me. I mean, I get the basic idea, but... It's a team, now? Was everyone on the team courting Bella, and Edward and Bella were like the quarterbacks? Were they each a team unto themselves, and those supporting them like cheerleaders? I'm just trying to understand the rules of this particular sport.