PHILADELPHIA — An arbitrator is sending Colin Kaepernick’s grievance with the NFL to trial, denying the league’s request to throw out the quarterback’s claims that owners conspired to keep him out of the league because of his protests of social injustice. Kaepernick’s lawyer Mark Geragos tweeted a picture Thursday of a ruling by arbitrator Stephen B. Burbank. The former 49ers quarterback argues that owners have colluded to keep him off any NFL roster since he hit free agency in 2017.