DJ Moore, a Carolina Panthers wide receiver, caught a 62-yard touchdown pass with seconds left in regulation to tie Sunday's game against the Atlanta Falcons.
But after celebrating by pulling off his helmet, Moore was given a 15-yard penalty for unsportsmanlike behavior.
The flag moved Carolina's Eddy Pieiro's extra point attempt from 33 yards to 48 yards. Pieiro missed the kick to the left, which would have given the Panthers a late lead.
Pieiro missed a 32-yard field goal for Carolina in overtime. Younghoe Koo's 41-yard field goal gave the Falcons new hope.
Interim coach Steve Wilks said after the Panthers' 37-34 loss, which brought their record to 2-6: "We've got to make sure that we're smart enough.
Moore, Walker added, "will learn from it." "I believe it is something that we will all learn from as a group."
Even if Moore hadn't been flagged, Pieiro might not have made the extra point, given that he missed a shorter overtime try.
How Moore and the Panthers scored concealed the touchdown's significance. Walker and Moore led Carolina to the end zone with 36 seconds left and a 6-point disadvantage.
Walker's 67.6-yard throw was the longest by air distance on completion since 2016, when Next Gen Stats was introduced.