The 10 moves that ultimately led the Patriots to sign James Harrison

Vilma: 'Harrison is there to provide intel on Steelers' (1:22)

Jonathan Vilma explains how James Harrison could help the Patriots should they face the Steelers in the playoffs. (1:22)

FOXBOROUGH, Mass. -- How did the New England Patriots find themselves in a situation where signing free-agent outside linebacker James Harrison on Tuesday -- a move that might have seemed highly unlikely at the start of the year -- was essentially a no-brainer?

Finally... A teammate that's older than me!😂😂 @tombrady

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The Patriots' defensive end/outside linebacker spot has been evolving all year, with the following 10 personnel moves playing a significant role in leading to this point:

1. Chris Long, who led all Patriots defensive ends in snaps played in 2016 at 65 percent, signed a free-agent deal with the Eagles in the offseason, saying he wanted a chance to return to a different type of defensive scheme.

2. Jabaal Sheard, who had the team's second-highest playing-time total among defensive ends in 2016 at 55.6 percent, signed a free-agent deal with the Colts as both sides seemed to feel a fresh start was best.

3. The Patriots acquired four-year veteran Kony Ealy and a third-round pick (No. 72) in exchange for a second-round pick (No. 64), with the hope that Ealy could possibly help fill the void created by the departures of Long and Sheard. But Ealy was released before the end of training camp as it was clear it wasn’t a good scheme fit.

4. After the first few days of training camp, veteran Rob Ninkovich -- who played 44 percent of the defensive snaps as part of a four-man rotation in 2016 with Long, Sheard and Trey Flowers (54 percent) -- announced his retirement.

5. Third-round draft pick Derek Rivers, a defensive end/outside linebacker from Youngstown State who projected as a rotation player, tore his ACL in an Aug. 16 joint practice with the Texans.

6. Their end-of-the-line ranks depleted with just Flowers and fourth-round pick Deatrich Wise (who currently has played 51.4 percent of the snaps) on the depth chart, the Patriots traded fifth- and seventh-round draft picks to the Seahawks for fourth-year defensive end Cassius Marsh on Sept. 2. But Marsh didn’t pan out -- he was undersized, struggled to consistently set the edge in the running game and too often ran past the quarterback in passing situations -- and he was released on Nov. 21.

7. On the same day, the Patriots signed first-year defensive end Eric Lee off the Bills' practice squad. In a reflection of how thin the Patriots have been at their end-of-the-line spot, Lee has since played 248 of a possible 338 defensive snaps (73.3 percent).

8. Undrafted outside linebacker Harvey Langi, a developmental prospect out of Brigham Young who flashed promise in training camp and was active for the Pats' Week 2 win over the Saints, was involved in a serious car accident in mid-October and placed on the non-football injury list.

9. Linebacker Dont’a Hightower, who didn’t play in the preseason as he recovered from a knee injury, was utilized in more of an end-of-the-line role upon his return to action. But he sustained a season-ending torn pectoral muscle on Oct. 22. That thrust Kyle Van Noy into a similar role, although he has missed the past three games with a calf injury. So most recently, that elevated undersized linebacker Marquis Flowers to play at the end of the line, where just-released Trevor Reilly had also taken some snaps.

10. Linebacker Shea McClellin, who opened the year on injured reserve, was designated to return on Nov. 8 in hopes that he might be able to help fill part of the void. But he experienced some type of setback and never was activated to the 53-man roster.