The 22-year-old is one of the most valuable young players in European football since exploding on to the scene in the 2015-16 campaign, after joining from MK Dons.
With 14 goals and 15 assists, Alli is enjoying an excellent season for Tottenham but has still often found himself the target of criticism from pundits and the media.
The England international, who managed 22 goals in all competitions last season - including 18 in the Premier League, nine more than his tally this time around - is perceived to have endured a dip in form in comparison to his heroics from the 2016-17 campaign.
But former Spurs hero Defoe, now at Bournemouth, just can't get his head around the abuse.
"Dele Alli -- I just can't understand why people give him stick. He's English and when you look at the numbers, the stats, they don't lie. Why would you say something negative about a young boy that's done so well?" he told ESPN.
"I just don't understand it. These people don't know him as a person. I do. He's one of the nicest guys you'll ever meet. He's just normal, a nice guy who loves his football. And that's it. He's gets a lot of stick and I think it's harsh."
Alli well and truly silenced his critics last month with a brace in the 3-1 win at then-Premier League champions Chelsea.
He is undoubtedly a class act, and a huge talent, but you could arguably question his consistency.
Scoring nine less Premier League goals this season is quite a significant downturn, but he is enjoying a career-best season in terms of assists, so you could also argue that his all-round game is improving, despite a reduction in goals.