IF THIS WERE just about the pass-catching skills of Eagles tight end Zach Ertz, there would not be an issue.

It's basically agreed that Ertz has the hands, speed and route-running techniques to be an impact player in the NFL.

Yesterday, at the Eagles' open training session at Lincoln Financial Field, Ertz made a couple of catches that elicited cheers from fans getting their first look at the 2015 Birds.

Still, there is a reason why, entering his third NFL season, Ertz has yet to have the breakout year that's been predicted since he was drafted in the second round in 2013 out of Stanford University.

A tight end also must be able to block, and Ertz' deficiencies in that area have prevented him from being on the field enough to become that impact receiver.

In his first two seasons, Ertz was on the field for 1,037 offensive snaps - only 48 percent of the ones the Eagles have run in that time.

By comparison, veteran tight end Brent Celek played 77 percent of the snaps in 2013 and 69 percent of them last season.

That's an issue for the Eagles, because, while Celek has been one of the toughest and most reliable players the Birds have had over his eight years, Ertz has the pass-catching ability to upgrade the offensive production from that position.

In the last two seasons, Celek has played 1,660 snaps. He's totaled 64 catches for 842 yards with seven touchdowns.

Over the same period, Ertz has 94 catches for 1,171 yards and seven touchdowns while playing 1,037 snaps - more than 600 fewer than Celek.

Celek isn't the receiver he was earlier in his career and it's clear that if Ertz were on the field more, he'd be the more productive pass catcher.

It's also clear that Ertz hasn't been on the field more because he's struggled in an area head coach Chip Kelly and offensive coordinator Pat Shurmur consider crucial to the offense being effective. Kelly values blocking in his tight ends and receivers. Those who can block are likely to run more plays than those who can't.

"Brent's an outstanding blocker," Kelly said late last season when the subject of playing time for the tight ends came up. "I think he may be the best blocking tight end in the league."

That's about as clear as it gets.

If Ertz wants more playing time in 2015, he must improve his blocking, maybe not to the level of Celek, but certainly to a level that garners more trust from the coaching staff.

To Ertz' credit, he's taken that challenge seriously.

Ertz' offseason included working on his blocking skills with former Dallas Cowboys offensive-line coach Hudson Houck.

He talked shop with future Hall of Fame tight end Tony Gonzalez - discussing the mental aspects of the game and developing a routine for transforming oneself from a good to a great player.

"I'm never going to be satisfied with where I am as a player," Ertz said. "I always want to improve in all my facets of the game, whether it's the receiving or blocking aspects.

"I'm never going to be satisfied whether I'm going into my third year or my 15th year."

Ertz even utilized one of the new offseason training techniques sweeping the NFL.

Training in West Hollywood at the Unbreakable gym run by Fox NFL insider Jay Glazer and co-owned by former Chicago Bears linebacker Brian Urlacher, Ertz is one of many NFL players who turned to mixed martial arts as a way to help their NFL careers.

In addition to things such as stretching, speed and weight training, workouts included boxing, wrestling and hand-fighting techniques taught by such MMA legends as Randy Couture and Chuck Liddell.

"You know we're not allowed to do the blocking stuff during the offseason," Ertz said. "We're not allowed to be on the field going up against one another, so you have to find other avenues to be able to train at blocking people in the offseason.

"This was an avenue I reached out for, and I think it's helped me a lot. Being in balance, using your hands and understanding leverage is what it all incorporates."

Yesterday was only the third day of training exercises for the Eagles and the first time they were in full pads, so it is too early to make any definitive statements about Ertz' improved blocking skills.

Still, even though noncontact OTAs and minicamps are not barometers of how things will go once Ertz is in an NFL game at NFL speed, Kelly said he likes the things he can judge.

" has done a great job, from a technique standpoint," Kelly said. "He's worked real hard, but we haven't had pads on.

"His footwork, hand placement and things like that have really improved, but now, when you get to days like this, hopefully things continue on.

"In what we could get accomplished with just helmets on in the offseason and now in the last couple of days, I think he's done a good job."