Dylan Hartley had only been on the field a few minutes before he was sent off by referee Jerome Garces for a violent (and incomprehensible) swinging arm shot across the neck of Sean O'Brien.
O'Brien had just scored a try to put Leinster 20-10 ahead when he was laid out on the turf by Hartley. TV audiences missed the incident in real time as their view was obscured by other players. The replays caught incident perfectly, however. Garces wasted no time in sending off Hartley.
The commentators then reported that O'Brien failed a head injury assessment after the assault from Hartley.
Leinster have since stretched their lead out to 32-10. They secured a bonus point through a try from Jamison Gibson-Park. (UPDATE: Isa Nacewa added another try to end the game at 37-10).
Fantastic close-up shot of Eddie Jones, head in hands, as he watched his captain trot towards the bench.
Hartley, in case anyone needs reminding, has attracted notoriety for biting Stephen Ferris, punching Rory Best, "making contact with the eye" of James Haskell and Johnny O'Connor. He was sent off in the 2013 Aviva Premiership Final for calling referee Wayne Barnes "a cheat".
Read more: The Bombshell, The Strike And The Outrageous Cockiness: Most Memorable Moments From Ireland v Australia
