Diggs was productive with the Minnesota Vikings, but their willingness to trade a young receiver who had signed a five-year contract drew some suspicion as to whether Diggs' attitude was the deciding factor in the split.
The Bills were willing to take that chance, and it has paid off in a big way. Entering Monday's game against the San Francisco 49ers (8:15 p.m. ET, ESPN), he ranks second in the NFL in receptions (80), sixth in receiving yards (945) and is on pace to set career and franchise highs in both categories this season.
"We did do some digging, and again, this guy's a super competitive guy and brings an edge to that position," Bills general manager Brandon Beane said in April. "I know diva gets put into [describing] that position a lot -- I would not call this guy a diva."
Part of that digging involved a conversation between Bills offensive coordinator Brian Daboll and Maryland coach Mike Locksley, who served together as co-offensive coordinators at Alabama in 2017.
Locksley recruited Diggs to Maryland in 2012 and they remain close, as do Locksley and Daboll. On the night the trade was announced on March 16, Daboll called his former co-coordinator to get some background on the new focal point of his offense's passing game.
"[Locksley] said it would be a perfect match -- him knowing me and Stef," Daboll said. "That's what I pride myself on, being real with these guys and just telling them things straight up and having their backs.
"That's all Stef craves. He's highly, highly competitive, he's very smart, he's a good teammate and he's real. Stef's real, he wears his emotions on his sleeves and that's what I respect about him.'"
Specifically, Locksley emphasized honesty with Diggs and said the receiver isn't the diva he might have appeared to be at times before his trade from Minnesota. But he warned problems can arise if Diggs feels betrayed.
"The only advice I gave to Brian about Stef was Stef is huge on trust," Locksley said. "That's where he and I are so much alike, in that he will give you everything he has if he knows that you care about him and he knows he can trust you to be consistent with who you are.
"When trust is broken with him, I will tell you that it's really hard to repair ... because he believes in loyalty and trust -- that's part of his DNA."
'The perfect community'
From Day 1, the relationship between Daboll and Diggs took off. Daboll and the Bills' coaching staff "put a lot on him," asking Diggs to play in several different spots within the offense.
It's a responsibility Daboll said a player has "got to be dialed in" to handle. But that's the exact mentality Diggs brings to a locker room.
He has done it since his college career, when he surprised the recruiting world by committing to Maryland in 2012 and turning down offers from Ohio State and Florida. His decision wasn't necessarily popular, given Maryland's 2-10 record in 2011, but Locksley said Diggs' "give-a-s--- gauge is on E" when it comes to others' opinions of him.
"Not too many guys wanted to go to Maryland back then," Diggs said. "And the ones who did were trying to do the same thing that I was doing and turn things around. ... For me, I'm definitely the kind of guy to not necessarily go against the grain, but I'm not always going to go with what everybody else is doing."
Randy Edsall has witnessed that side of Diggs firsthand. He coached Diggs at Maryland from 2012 to 2014 and said much of the misconception surrounding Diggs' mentality stems from not understanding his competitive nature.
"I think sometimes people take guys the wrong way who have that innate trait," Edsall said.
Edsall used one game as an example.
Maryland traveled to play Penn State during Diggs' final season. The Nittany Lions were 4-3 at the time, but any game in Beaver Stadium is a chance to make a statement -- and that's exactly what Diggs, a junior, tried to do.
"Before the game, he was one of the captains and he told the other two [Maryland] captains, 'We're not shaking their hands at the coin flip,'" Edsall said. "He knew what that was going to be, but he was going to make a statement -- and we ended up winning. I think that's good, but you have to understand that personality within Stefon."
It all stems from belief in his abilities.
"When a guy like Stefon decides not to go to one of the perennial powers in college football, it goes back to show the confidence he has in himself," Locksley said. "And not every kid is built to do that, because peer pressure still runs recruiting. ... If your friends don't think it's cool, then most people aren't built to handle the negativity that comes with it.
"He's confident enough in himself that, 'wherever I go, I'm going to make it a better place.'"
It's similar to the attitude surrounding his trade to Buffalo. Critics of the trade were skeptical Diggs could thrive in the Bills' 26th-ranked passing offense from 2019.
But he succeeded at Maryland, where he went to two bowl games and led the team in receiving yards (848) and all-purpose yards (1,904) as a freshman. And so far, he has found success in Buffalo.
"I've always been a winner in my heart. ... I'm always going to do everything in my power and give it everything I've got," Diggs said. "No matter what team I'm on, I try to do that. Going into Buffalo and my new situation, a lot of people weren't too high on Buffalo, people on the outside.
"But none of that s--- really matters to me. I like the guys that I'm around, I appreciate the guys that I'm around. They grind, they put the time in just like any other team."
Based on what he knew about the Bills, that's why Locksley thought his former pupil was headed for the perfect situation.
"He is the ultimate competitor, this guy loves to compete. You will never find a guy that will work harder in the offseason," Locksley said of Diggs. "He doesn't have a lot of hobbies, his hobbies are fashion and perfecting his craft. He's always in shape, was never a big club guy -- I thought Buffalo was the perfect community for him."
'He's a grinder'
The consensus from Bills players and coaches is Diggs has made an impact beyond the stat sheet.
During his season-high, 153-yard performance against the Miami Dolphins in Week 2, Daboll said Diggs spent halftime lobbying for ways to get fellow wide receivers Cole Beasley and John Brown the ball. In the waning moments of the Bills' loss to the Kansas City Chiefs in Week 6, cameras caught Diggs on the sideline -- not pouting or angry, but encouraging his teammates.
Beane praised Diggs' mentality in April, something the front office and coaching staff were eager to see when the wide receiver arrived in Orchard Park.
"I want him to be him. I don't want him to be anything else but him," Daboll said. "He's got juice, he's got fiery competitiveness, he's got swagger -- and I want him to have it because it rubs off on our team.
"He's an old throwback. He wants to grind at practice, you've got to take him out because he just wants to keep going. And if it's not right at practice, he gets hot. He's just been such a pleasure to be around."