So much of the legend of Kiko Alonso.

Less than two years after Alonso burst out of the gate as a rookie and became a fan favorite for his carefree personality, the Buffalo Bills and Philadelphia Eagles worked out a deal Tuesday to swap Alonso for three-time Pro Bowl running back LeSean McCoy.

Rarely do player-for-player trades happen in the NFL, but this one makes plenty of sense for both sides, as long as McCoy is happy with the deal. A source to McCoy told ESPN's Josina Anderson that McCoy is "frustrated" and is "not going to make it easy. That's for sure." So stay tuned on that end of the story.

But assuming the deal is finalized next week, the Eagles will clear most of McCoy's $11.95 million cap hit off the books and will have a shot to find another stud running back in what's considered a deep draft class this April. Coach Chip Kelly is also reunited with Alonso -- one of his former players at Oregon -- who comes at a cheap price and brings plenty of upside to the Eagles' defense.

The Bills address one of their biggest offseason needs by adding McCoy. With Fred Jackson turning 34 last month and C.J. Spiller set to hit free agency this weekend, the Bills needed an infusion of talent at running back. McCoy is one of the most talented at his position in the NFL.

It just makes sense.

McCoy tallied nearly 1,500 all-purpose yards last season and eclipsed 2,100 all-purpose yards in 2013. He's only 26 and should have enough tread on his tires to play out the final three years of his current deal, and probably longer.

The question for the Bills will be their ability to block for McCoy. There were some issues with the Eagles' offensive line last season, which caused McCoy's average yards before contact per rush to drop from 3.59 in 2013 (second best in the NFL) to 2.71 last season.

The Bills' offensive line was a mess last season, and, even though they've already added Richie Incognito this offseason, they'll need to do more to upgrade that unit.

The good news is they'll have more flexibility in the draft to address their other needs. A week ago, I would have pegged running back as one of the Bills' top draft needs and considered it a serious possibility they'd take one with their second-round pick, their first of the draft.

Now, they don't need to draft a running back until the late rounds, if at all. That means quarterback, tight end and offensive line come to the forefront for the Bills' second- and third-round picks this April.

The Bills will take a $10.25 million cap hit by acquiring McCoy and save less than $1 million by trading Alonso, so the Bills' cap space -- which NFLPA records listed at $27.1 million earlier Tuesday -- will be cut considerably. Re-signing defensive end Jerry Hughes will put another dent in that number and limit what the Bills could do elsewhere in free agency.

Still, the point of free agency is to acquire good players. The Bills were able to do that Tuesday by agreeing to the deal for McCoy, so the fact that their spending power this March will be limited because of the trade is hardly a setback.

The impact on the Bills' defense shouldn't be substantial, either. They lose a cheap, rising young player in Alonso but they already have a replacement: Preston Brown, a 2014 third-round pick who played the second-most snaps of any defensive rookie in the NFL last season and held his own.

If there was any position at which the Bills could afford to lose a player such as Alonso, it was linebacker. And truth be told, the Bills got by just fine without Alonso last season. With strong performances from Brown and Nigel Bradham at linebacker, they were considerably better in run defense, jumping from 28th in yards allowed per game in 2013 to 11th last season.

Unless McCoy gives the Bills headaches all summer about coming to Buffalo, or if he drops off a cliff after posting four 1,000-yard rushing seasons in his first six years in the league, there is little reason to fret about this trade.

Savor the moment, Bills fans, because it's not often that teams can draw up player-for-player swaps that make this much sense for both sides.