There are a lot of variables in Thursday's first round of the NFL draft, from which team will roll the dice on Johnny Football to whether there will be a run on offensive tackles like last year.

Some even think the Houston Texans will be foolish enough to pass on defensive end Jadeveon Clowney, the best defensive prospect in the past eight years (Mario Williams), if not the past 29 (Bruce Smith).

But there is one certainty. Raiders general manager Reggie McKenzie needs to hit a home run with the No. 5 pick. He and head coach Dennis Allen are 8-24 in their first two years, and though owner Mark Davis said he is patient, he would like to have seen more progress.

"We have to find somebody in the draft or in free agency that is going to be the identity of the Raiders," Davis told the Chronicle at the NFL combine. "I don't know if we really have an identity now."

McKenzie added some pass rushers and cornerbacks, power-blocking-suited offensive linemen and quarterback Matt Schaub, running back Maurice Jones-Drew and receiver James Jones in free agency. The next three days, he needs to get some young playmakers ... and he definitely has the opportunity to do that with two of the first 36 picks.

Receiver Sammy Watkins and outside linebacker Khalil Mack both could be franchise players and either could be available for the Raiders. (Clowney will be long gone.)

Watkins, of Clemson, has rare speed and soft hands, and capped his college career with 16 catches for 227 yards and two touchdowns against Ohio State in the Orange Bowl. Mack played for a small school (Buffalo) but also had one of his best games against Ohio State. The 6-foot-2, 258-pound Mack has an explosive first step and can rush the quarterback as well as drop back in coverage.