Harvin last played for the Bills in 2015, before hitting injured reserve in November with multiple injuries (although reports at the time indicated his issues might not be "strictly injury-related"). Harvin didn't travel with Buffalo to London and eventually retired at the age of 27 this past off season.
Now he's back in the game, joining Buffalo again in his third stint with a Rex Ryan team. With Sammy Watkins out and the Bills' top wide receiver being Robert Woods, it's understandable the Bills would be interested in seeing if Harvin can step in and produce for the passing game.
The beauty of Harvin is his production is athleticism-based, which means he doesn't need a ton of practice in a system to make him effective. Put him in the backfield -- the Bills are also dealing with injuries to LeSean McCoy -- or let him operate in bubble screens.
Optimism for Harvin might be asking a bit much though. He said he would have his best season ever before 2015 and that wasn't the case. There were reports he would play again this year, but they never came to fruition.
In the last three years, Harvin has 718 receiving yards and two touchdowns. Expecting him to be a difference-maker after taking months away from the game is asking a lot.
Harvin's entire history in the NFL is pretty wild. He is the ultimate modern NFL talent who never lived up to what people wanted from his skill set. Drafted in the first round by the Minnesota Vikings in 2009, Harvin would do things people other people couldn't do.
My personal favorite Percy Harvin GIF:
How can you not be enamored by that play??? The Seahawks certainly were, trading a first-round pick for Harvin. He wouldn't play much for Seattle, but did break a kick return to the house in the Super Bowl that they won, so he served as the world's most expensive victory cigar -- they also gave him a six-year, $67 million contract -- until he started breaking up Seattle's locker room and they sent him to the Jets in a deal.
Harvin was later released and would sign on with the Bills before 2015. If he can make any impact at all for Buffalo, it's a big plus.