The injury brought back memories of former Richmond player Nathan Brown's infamous awful broken leg sustained against Melbourne more than a decade ago, when his leg went floppy in the face of a smother while trying to kick.
"It's the Nathan Brown injury of many years ago," said Fox Footy commentator David King.
"It's a horrible injury."
Despite still being so young, Wallis has become one of the Dogs' leaders in recent times - in particular last year when he stepped up to fill the void left by Tom Liberatore's absence.
He made his senior debut in 2011 after being recruited courtesy of the father-son rule, his dad being club legend Stephen Wallis.
He's played 92 games and kicked 41 goals in the blue, white and red.
Wallis' injury couldn't inspire his side to victory though, as St Kilda recorded their most-important victory of the season, downing the Bulldogs by 15 points at Etihad Stadium.
Skipper Nick Riewoldt booted four goals to help the Saints bank three straight wins for the first time since 2011.
They sit eight points behind eighth-placed North Melbourne on the ladder and remain an outside chance of contesting the finals this year. The Bulldogs' top-four hopes took a hit while they finished with one fit man on the bench, losing 11.9 (75) to 9.6 (60).
Veteran defender Dale Morris played no part in the second half, further stretching an inexperienced defence that was struggling to contain Riewoldt. Jack Redpath was also hurt in the final quarter.
The Bulldogs failed to score in the final term.
Morris' setback came as Riewoldt threatened to bust the game wide open.
Riewoldt kicked three goals in a run of five consecutive goals from the Saints, who led by 19 points in the third quarter when Tim Membrey missed a simple set shot.
It was the biggest lead enjoyed by either side in a very tight tussle and St Kilda looked set to kick clear.
But the Bulldogs rallied with three goals in the space of two-and-a-half minutes.
Marcus Bontempelli, who was the Bulldogs' best player with 25 possessions and three goals, helped level the scores.
St Kilda steadied with the next two goals of the match, thanks to Nathan Wright and Jade Gresham, and the Bulldogs were unable to respond.
The Bulldogs dearly missed injured forward Jake Stringer, their leading goal-kicker for the season.
Both sides looked to move the ball at breakneck pace and applied fierce pressure, resulting in a slew of turnovers but also some brilliant passages of play.
Saints midfielder Jack Steven was involved in plenty of those highlights.
Steven finished with 39 disposals but tallied 26 of them in a scintillating first half.
