Is defensive coordinator Chip Kelly's most important hire?

SANTA CLARA, Calif. -- Jim Tomsula had a bit of a challenge filling out his coaching staff last winter, with the San Francisco 49ers staff taking on a certain NFL Europe feel as a result.

Might new Niners coach Chip Kelly be facing a similar situation?

It’s early in the process, sure, but Mike Vrabel turning down Kelly’s offer to become his defensive coordinator and instead remain the Houston Texans' linebackers coach is not a good look.

And with word coming later Friday that Kelly had chosen to fire Eric Mangini, the sitting defensive coordinator, the chance at continuity seems to have disappeared for a unit that is going to need all the help it can with Kelly’s fast-paced offense.

From that vantage point, defensive coordinator is the most important hire Kelly is going to make, and you might say he’s already 0-for-2. Yes, I realize Mangini was technically fired by Kelly, but Mangini represented familiarity and probably should have been given the opportunity to improve his defense, which was not the Niners’ glaring issue last season and showed flashes despite finishing 29th in total defense.

So what does Kelly, who said he will keep the Niners defense in a base 3-4 alignment, want in a defensive coordinator? After all, Kelly’s offense averaged a play every 23.1 seconds of possession in Philadelphia last season, nearly three seconds faster than the next-quickest team, and a league-low average time of possession of 26 minutes, 6 seconds.

The seeming result on the other side of the ball?

The Eagles' defense was gassed in the second half of games, particularly in the latter part of the season.

Consider: Philadelphia fell from 22 first-half sacks last season to 13 sacks after halftime under Kelly and the Eagles gave up 36.0 points and 450.2 yards per game in Weeks 11 through 16, before he was fired with one game to play.

“I’m just looking for a defensive coordinator that can shut people out,” Kelly said with a Cheshire Cat grin following his introductory news conference Wednesday.

The conspiracy theory making its way around Santa Clara is that because Kelly is tight with New England Patriots coach Bill Belichick, noted Belichick enemy Mangini had to go, what with his role at the epicenter of Spygate.

That would also explain Kelly’s fascination with Vrabel, who played eight seasons for Belichick in New England.

Regardless, the Niners’ official stance on why they chose to wait six days between Kelly’s hiring and his presser was so he could focus on compiling his staff.

Thus far, his lone hires, which have yet to be announced by the 49ers, are Curtis Modkins as offensive coordinator, though Kelly himself said he would be calling in plays from the sideline, and Pat Flaherty as offensive-line coach.

The defense, though, is what needs Kelly's immediate attention.