San Antonio lost Cory Joseph to the Raptors in free agency and needed a third point guard behind Tony Parker and Patty Mills in case of injuries. No names emerged in free agency rumors but the need for depth at the position was evident. The Spurs could have settled for a veteran on his last legs but have instead traded for the 36th pick of the 2013 draft. His salary is non-guaranteed so the Spurs could trade him later on -- perhaps packaged with Reggie Williams' non-guaranteed deal -- or waive him if he doesn't pan out.
McCallum is 24 years old and has played in Sacramento for the past two years. He never blossomed as a legitimate backup with the Kings but showed progress in his second season in many areas. He has decent size for the position, standing at 6'2", but doesn't possess a large wingspan. He's still a scrappy defender but will likely be a downgrade over Cory Joseph in that area.
Offensively McCallum struggles with his three-point shot and is not a particularly prolific playmaker but he can run a team. He can finish inside and could develop into a good backup. With Darren Collison in place and the addition of Rajon Rondo, the Kings simply didn't have room for a project.
McCallum averaged seven points and three assists on 44 percent from the field in 21 minutes a game last season. He started 30 games for the Kings and finished strong once George Karl was in tow, averaging over 11 points and four assists since March. The Spurs' roster now stands at 12, including Williams.