PFL's 2019 playoff brackets will be locked by the end of Thursday night at PFL 6, as the big boys -- the heavyweights and light heavyweights -- get last licks.

There were some surprises back on June 6 when those divisions competed for the first time, as light heavyweight favorites Vinny Magalhaes and Jordan Johnson suffered losses to Emiliano Sordi and Maxim Grishin, respectively. Jared Rosholt, a top heavyweight, was stopped by Denis Goltsov.

Do those results represent a changing of the guard? Magalhaes and Rosholt had playoff runs last year, and Johnson was undefeated in the UFC. We'll find out a lot more Thursday night, and we'll also see the PFL return of Khabib Nurmagomedov's cousin, Umar Nurmagomedov, in a non-tournament bout.

Let's take a look at the top five storylines to watch going into PFL 6.