On Sunday, the Houston Texans changed their quarterback situation. What exactly that means, we don't know just yet.

They released Case Keenum, a player who started eight games last season but was still very much in a developmental stage. They traded for Ryan Mallett, a New England Patriots third-round draft pick in 2011, giving up a draft pick that will be either a sixth-round or seventh-round pick, depending on playing time.

Mallett gives the Texans another option in a fairly low-risk move, and he wasn't brought to Houston to be just a space-filler. But right now, the questions about the Texans' quarterbacks still outnumber the answers.

Playing behind Tom Brady, Mallett never had more than garbage-time reps during regular-season games in New England. His college history was spotty as well, with off-the-field questions that dropped him to the third round.

O'Brien knows Mallett better than most coaches in the NFL. He was the offensive coordinator and quarterbacks coach in New England during Mallett's rookie season. O'Brien would not have made this move without being comfortable with both Mallett's ability and his commitment.

Without having seen what Mallett can do, though, there remains only one quarterback on the Texans' roster who is a known quantity: starter Ryan Fitzpatrick.