With a cross coming into the box, the Manchester City defender threw his arm up and caught the Tunisia attacker in the face, with Ben Youssef immediately going to ground.
The referee didn't hesitate to point to the spot, and Ferjani Sassi buried the ensuing penalty to make it 1-1.
Was Walker the victim of a soft penalty call or was he, as some on social media claim, "brainless"?
As always, there was plenty of debate.
Soft penalty! Yes
Can you give? Yes
Walker silly right there? Yes
Why he didn’t jus head the ball away? Don’t know — Jan Aage Fjortoft (@JanAageFjortoft) June 18, 2018
Say what you will about it being a soft penalty to award, but Kyle Walker is utterly brainless to put his arm out like that. Needless. — Leanne Prescott (@_lfcleanne) June 18, 2018
Pure stupidity from Kyle Walker. Brainless — James Pearce (@JamesPearceEcho) June 18, 2018
It was a penalty. Hard to see what Walker was doing there swinging his arm like that. Referee had a good, clear view and stopped in his tracks to point to the spot. @MirrorFootball — Darren Lewis (@MirrorDarren) June 18, 2018
I don't know how Walker's foul there was Sterling's fault, but I'm sure we can blame him somehow.— Sam Kelly (@HEGS_com) June 18, 2018
Soft or not, stupidity from Walker. — Daniel Storey (@danielstorey85) June 18, 2018
Despite a number of good chances to add another goal, England went into half-time level at 1-1.
The Three Lions would end up taking all three points late, as Harry Kane scored his second goal of the game in stoppage time to give his side a 2-1 win.