Pryor is an NFL athlete. There is no doubt about that. He stands 6'4", weighs nearly 240 lbs, and runs an electric 4.38 40-yard dash. Some have him clocked at 4.33. To provide some perspective, only six players in the upcoming draft were clocked at 4.38 or faster; only two players were clocked at 4.33 or faster. None of those players were taller than 6'0" or weighed more than 202 lbs. His closest recent comparable might be Patrick Peterson who, at 6'0" and 219 lbs, ran a 4.34 in 2011. Robert Griffin III ran a 4.41 at 6'2" 223 lbs in 2012. You have seen how fast RG3 is. Now take a look at Pryor at game speed.
Middle Scramble - Watch how he accelerates past the second level of the defense.
Bootleg - Notice the power at the end of the run.
The idea that Seattle brought him into to compete for the backup quarterback role is bit of a stretch. The best things he would bring to that position would be a lower salary than Tarvaris Jackson by a few hundred thousand, youth, and a better scout team representative of the scrambling quarterbacks in the league like Colin Kaepernick. The Seahawks don't need to practice against a Kaepernick to beat a Kaepernick. They have proven that repeatedly.
Pryor is too unpolished as a passer to expect him to round into form in just one season, which is all he has left on his rookie contract. And the Seahawks have not shown the ability to develop quarterbacks. Russell Wilson is not a significantly different player now than he was when coming into the league, and the improvements in his game appear to have as much to do with his own study and work habits as coaching.
Pryor is quick to bail on a play and start running. The above highlights show why. The other reason is he was an erratic and inaccurate passer, and did not show a propensity for reading a defense. If he is going to be a quarterback for Seattle, I would think it would be the third, not the backup.
It is always fun to start trying to move a great athlete like Pryor around to get his talent on the field. The reality is that very few players make the transition from quarterback to another position at the NFL level. Carroll and his staff will see that as a challenge. They showed immediate interest in Jermichael Finley when he became available this off-season, but his medicals did not pan out. Pryor is roughly the same height, considerably faster (4.67 vs 4.38), and not completely out of weight range (247 lbs vs. 233 lbs). Expect the Seahawks to see if he can play some tight end or big receiver. Running routes and blocking, though, are not things that just happen for most players. It takes years to develop those skills. Then, there are some more far-out notions of where he could fit.
The Seahawks signed Phillip Adams to play slot corner, and he is also a punt returner, but not so dominant at it that the job is decided. Pryor is the type of of athlete that could potentially bring a Patrick Peterson-like toughness and electricity to the punt return game.
H-Back / Fullback
Seattle has already been experimenting more and more with tight ends in the back-field instead of fullbacks. Imagine a back-field that consisted of Percy Harvin and Pryor or Christine Michael and Pryor or Marshawn Lynch and Pryor flanking Russell Wilson. Pryor plays tough from what I have seen. He invites contact. Adding yet another explosive athlete to the backfield could put defenses in a world of hurt trying to contain all the various options vertically and horizontally. Not to mention, two quarterbacks in the back-field makes for some other interesting possibilities.
Low Risk, High Reward
Seattle gains an athlete that has more upside than anyone they would have drafted in the 7th-round in two weeks. They only have him for this one season, so they are not looking to develop him. They are looking for a way to get him on the field this year. His ability as a quarterback is a bonus. Training camp just got a lot more interesting.