Allen played the first four seasons of his NFL career with the Chiefs, who selected him in the fourth round of the 2004 draft. Those were productive seasons, as Allen totaled 43 sacks and led the league with 15.5 in 2007, his last season in Kansas City.
But Allen was unhappy with what he perceived as unfair contractual treatment from the Chiefs and he forced a trade to the Minnesota Vikings for one first-round and two third-round picks in the 2008 draft.
Allen received the contract he was looking for from the Vikings and his career continued to flourish after he left Kansas City. Allen led the NFL once more in sacks, with 22 in 2011. He later played with Chicago and Carolina and his final NFL game was Super Bowl 50 with the Panthers. He finished his career with 136 sacks, including seven consecutive seasons of double-digit sacks.
The Chiefs, for their part, struggled in their first couple of years without Allen, winning a total of 10 games. Their pass-rush production slowed to a trickle without him, at least initially. The Chiefs had 10 sacks as a team in 2008, the same year Allen had 14.5 for the Vikings.
The Chiefs used that first-round draft pick obtained from the Vikings to select Branden Albert. He was their starting left tackle for six seasons and was shaky at the start of his NFL career before playing at a Pro Bowl level his last couple of seasons in Kansas City.
The Chiefs used one of those third-round picks from that trade to select running back Jamaal Charles, who has gone on to become one of the elite backs of his time. He is the Chiefs’ all-time leader in career rushing yards and, assuming all continues to go well with his rehab, will play for the Chiefs again in 2016 after missing much of last year with a torn ACL.
The post-Kansas City portion of Allen’s career worked out well for him and the Chiefs got something of great value from the trade as well. That makes the Allen deal a classic case of win-win.