The new coach’s press conference on Sunday was notable for the depth with which he discussed the slot receiver position and the Niners’ leading candidates for that job.

The slot receiver position means more to Chip than most coaches. He loves to use “11 personnel,” with one running back, one tight end, and 3 receivers. The Eagles ran 11 personnel 71%, 65% and 69% of the time in 2013, 2014 and 2015 respectively.

For many coaches this is a passing formation common on third down, but Kelly also likes to run out of it on early downs, following spread offense principles. Last year the Eagles used 11 personnel on 54% of first down plays, and 66% on second downs. Teams often go to their nickel package against 11; this lightens the box and typically replaces a linebacker with a DB.

Now the defense faces a dilemma. If they respect your receivers, they have to open up possibilities for running. If not, you can pass to one or your receivers or an RB on a wheel route or screen.

There is another advantage to running out of 11 personnel. If the offense falls just short on 3rd down, Kelly’s flexible formation can quickly line up to go for it on fourth down without substitution. The prevents the defense from subbing in a beefier front line to stop the short run.

Last year though, the weakness of the front line forced the Eagles to run more “12 personnel” (with 2 receivers and 2 tight ends) in the second quarter of the season.

Of course, there is also the aspect of raw talent. The Niners aren’t overloaded with skill at either the TE or WR position, but WR Eric Rogers is out for the season with an ACL tear and fullback Bruce Miller has shifted to tight end since Kelly never uses a blocking back. If the Niners end up with two or three strong tight ends and no one steps up to join Torrey Smith out wide, Kelly may go with more 12 or even 13 or 03 personnel.

At Sunday’s press conference, Kelly first was asked what qualities he seeks in a slot receiver. (Beat reporters have figured out that asking Chip general football questions rather than details about individuals is a great way to get him to expand.)

“Well, the number one quality is, how can he win in one-on-one situations? And there’s big guys that do it kind of because they can outmuscle you. Sometimes, the nickel slot corners in this league are smaller, so sometimes it’s beneficial to have a big guy and we’ve had success with big guys in the past. Or, if you’re a young guy, not a young guy, a smaller guy, can you separate. It’s really the ability to operate in the middle of the field. ... The ability to negotiate traffic. Have an understanding of zone. Have a really, really good spatial understanding of zone coverages.”

In Philadelphia, 6’3” Jordan Matthews was the only new receiver under Chip who accomplished much. Kelly kept him in the slot because he liked the matchup problem he presented against typically shorter slot CBs, especially when he had a speedster (DeSean Jackson or Jeremy Maclin) out wide.

That does not appear to be his plan for the Niners, though. Kelly has been playing 5’9” Bruce Ellington, 5’11 Bryce Treggs and 6’0” DeAndrew White in the slot so far. Asked about this change, Kelly may have dropped a hint that he plans to run more 12 personnel and less 11 this year.

Q: How come you don’t have any of your bigger wide receivers working out of the slot right now? Will that happen over time? A: Maybe over time, but I think when we first got going, it’s let’s get guys kind of slotted, because you’ve got ‘X’ amount of reps. So, to put four or five guys in there, they’re not going to get as many reps. When you’re in 11-personnel they get all the work, but if you go to two tight ends, those slot receivers are off the field. So, when you start to get into some different personnel groupings, you’ve got to be mindful of how many reps you have that can go to that inside receiver.

Then the coach was asked about the specific receivers he has inside. His description of Bruce Ellington was particularly interesting.

“I think the first thing with Bruce, and it relates to he’s got his background as a basketball player. So, he understands spacing, he understands how to attack a zone, he understands where the soft parts of a zone are. There’s a correlation between guys who played basketball or have a basketball background and then kind of understanding how to operate in there. So, I think he’s got a real good feel for working in the slot.”

Three of the NFL’s best tight ends (Martellus Bennett, Travis Kelce and Jimmy Graham) are former basketball players, so maybe there is something to his theory.

Q: What about WR Bryce Treggs, you watched him at Cal right? Did he stand out to you during that workout as someone who could work out here? A: He did because I think he’s got great short-area quickness, to go along with some long speed. He can really run and stretch a defense. He has the ability to kind of separate inside in there just because of his short-area quickness. He was a guy that we felt would fit in the mold. He’s a lot similarly built, similarly sized to Bruce. They both kind of have the same qualities in there.

The Eagles struggled at wide receiver after losing Jackson and Maclin; 2015 first round pick Nelson Agholor was a major disappointment. It appears that Kelly is looking to emphasize speed in his receivers, perhaps to make sure that situation doesn’t repeat. A spread offense works a lot better with deep speed pulling the safeties back, and Kelly found out the hard way that wide receivers aren’t as easy to replace at the pro level.