PITTSBURGH -- Over a span of four days, James Harrison went from the Pittsburgh Steelers' favorite helmeted hulk to a roster cut to a selfie-snapper with new teammate Tom Brady in the New England Patriots' locker room, finding himself on the other side of a potential Patriots-Steelers collision in the playoffs.

How did this happen?

Steelers coach Mike Tomlin said he simply needed a roster spot for the return of Marcus Gilbert and wanted to keep the other players. That probably doesn't tell the whole story.

But surely the Steelers must have known the Patriots, with their well-known affinity for scooping up unhappy players, would pounce on Harrison, who at 39 is now New England's second-oldest player.

James Harrison didn't play much this season with Pittsburgh, but he could potentially give a boost to the Patriots' pass rush. Scott Winters/Icon Sportswire

Harrison's signing with New England can impact the Steelers, since the player still has a few transferable skills on the field, but Steelers fans might be giving New England too much credit.

The likelihood of Harrison clinching a Patriots Super Bowl berth with a Ben Roethlisberger sack is not very high.

He can still play, but this is mostly a matchup flier after the Steelers played him on just 40 snaps through 14 games.

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The reaction I got from a few Steelers people Tuesday night was mostly indifference while acknowledging the business side of football. They greatly respect Harrison and feel he should be free to sign with anyone. After all, he was released. Take the next job available. One player commended Harrison for double dipping on salary. Harrison got a $500,000 signing bonus and most of his $1.2 million salary from his two-year deal with Pittsburgh, then claims a per-week clip of about $58,000 with New England (the $1 million veteran minimum split per game).

Sure, Harrison might have inside information from Pittsburgh's locker room that could aid the Patriots. But the Steelers largely believe the two teams know each other well enough, anyway, and the intel game can be overblown. Maybe he's got an offensive line tell he can relay to Bill Belichick. In that case, Harrison's role might be more valuable as a de facto scout than a player. But the Steelers don't seem worried about that.

Harrison is not an every-down player but can rush the passer situationally and help against the run. New England needs help on both of those fronts. The Steelers don't. The outside linebacker trio of T.J. Watt, Bud Dupree and Anthony Chickillo made Harrison expendable.

New England might be signing Harrison more for another matchup, such as Kansas City in the divisional round. Harrison has had success against Chiefs left tackle Eric Fisher. This might not be about Pittsburgh at all.

If Harrison does get a crack at the team for which he totaled 80.5 sacks, he'll be highly motivated to get into the backfield and greet old friend Roethlisberger. An intriguing matchup would feature Harrison against left tackle Alejandro Villanueva, who has seen plenty of Harrison in practice settings over the years. Villanueva has credited Harrison for helping him develop as a tackle. Both sides would know each other's tendencies, but Harrison's rush game is power, which typically isn't a problem for Villanueva, who sometimes has trouble with speed.

Harrison is a juicy subplot for the league's best playoff matchup. But the same players who determined the Week 15 clash -- Roethlisberger, Brady, Gronk and more -- will remain in starring roles and might not have room for another.