I've been asking this for a while. They have a good TE in Celek, they sign FA Casey and then draft Ertz in the second. Then they don't use them the way we thought the would. It seems it's just what Kelly has said all along, it depends on the defense and they "take what they give 'em."
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Philadelphia faces base defense only 16% of the time. Opponents go to nickel on fully 82% of the Eagles' run plays, barely less than on passing downs (85%). Detroit (64%), Denver (58%) and Green Bay (54%) are the only other teams facing nickel on more than 50% of runs.

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Kelly values versatile players, and drafted Zach Ertz in part because he has the speed (After running the 40-yard dash in the 4.65 to 4.76 range back in Indianapolis at the NFL Combine, Ertz improved that to as good as 4.57 on Thursday in front of scouts from all 32 teams. Ertz also put up a vertical leap of 30 inches at the combine, but improved to 35 inches at the Stanford Pro Day.) and moves to (eventually) play a legitimate wide receiver in the NFL, as well as the size and blocking to play a traditional tight end. At that point, how will you even tell if the Eagles are in 11 or 12? If Ertz is in the slot, what position will he be playing?