Muir was recruited by St Kilda in the middle of the 1974 season. but would only play another 18 games in the next four seasons. Muir's ability as a footballer was confirmed by
Ron Barassi who described him as one of the VFL's most talented players. Len Templar said "There was no better player than Muir. ... He could have done anything".
Neil Roberts, who Muir reveres for his friendship, said "He's not a fellow, he's a happening". St Kilda's official history says "[Muir] played football with a cyclonic power that was allied to one-touch skills". Muir was given the nickname "Mad Dog" by team-mate
Kevin Neale who thought Muir ran around the field "like a sheep dog ... mad". The name stuck and later became associated with the numerous acts of on-field violence perpetrated by Muir. Muir would later disavow the name saying "... the blackfella thing came into it. It was terrible" and "I don't want people to say, 'There goes Mad Dog.'" Former AFL coach
John Northey, who mentored Muir in Ballarat, was very critical of the name, saying "I think Robert is more maligned than any player who's ever played the game. I think it put him in positions he shouldn't have been in". Muir's time at St Kilda was marred by constant racial abuse from opposition players and supporters and a lack of understanding of his predicament from his own club. Muir himself said "I just answered (racism) probably the wrong way and belt them back ... They wouldn’t say it the next game so you'd shut them down that way. [...] We didn’t have vilification rules, no lawyers, counsellors, didn’t have that. You're basically just left on your own, to your own devices." Towards the end of his first spell at St Kilda in 1978, Muir was reported for kicking his opponent in a reserves game against South Melbourne for which he received an eight-week suspension. In defending him at the tribunal, his advocate relied on racial stereotypes - to the disgust of Muir. Muir transferred to
West Torrens Football Club in the
South Australian National Football League (SANFL) for the 1979 season. While at West Torrens, Muir was suspended for four matches for striking
North Adelaide captain
Barry Stringer and was acquitted of a charge of striking an umpire. Muir returning to St Kilda in 1980. Later that season, in a match against
Collingwood, Muir was again reported for striking
Ray Shaw. Muir claims that he was the victim of racial vilification all match from both Collingwood players and supporters. Muir showed obvious distress during and after the match. Collingwood fans abused Muir outside the change rooms at the end of the game. Journalist for
The Age, Alan Attwood described the supporters as "hyenas round a cornered prey" while "baiting and abusing [Muir] in the lowest manner". Muir required a police escort to leave the ground but this did not stop his windshield being broken by a thrown bottle. At the tribunal Muir claimed he was spat on by Shaw. This was denied by Shaw and Muir was suspended for four matches. An anonymous teammate told the
Truth "It isn't only Collingwood ... [racial abuse] happens to Robert all the time, and we're powerless to do anything to help him ... they're ruining a fine player". At the end of 1980, Muir left St Kilda, returning to Ballarat for a while and then later settling in Adelaide. Muir returned to St Kilda in 1984 at the request of coach
Tony Jewell, who allowed Muir to train in Adelaide and fly in to
Melbourne for matches. In a reserves match in
Geelong in April that season, Muir responded to persistent racial taunts from Geelong senior players over the fence - giving them "
the finger" and ripping off his jumper to show them his black skin. Muir kicked seven goals that game. Later than season, Muir played
Carlton at their home ground
Princes Park, Carlton. In a spiteful match, where Muir claims he was repeatedly racially vilified by his Carlton opponents - "every five or 10 minutes" - Muir was reported for violent conduct seven times. Despite Muir's misgivings, St Kilda and his advocate at the
tribunal chose to use a defence of provocation by the racist abuse. Muir's defence included an impassioned plea from
Mollie Dyer from the
Aborigines Advancement League and fellow Aboriginal player
Maurice Rioli spoke in Muir's defence stating "Robert can't accept [racial abuse] as a tactic [by opponents] like myself." Muir was found guilty of six of the seven charges and suspended for 12 matches. Muir's mother Myrtle later spoke to
The Sun News-Pictorial: Muir told the same newspaper later "We do hear the supporters [make racist remarks] a bit, but it hurts when it comes from the players themselves. It shouldn't be allowed to go on". Muir signed with SANFL club
Woodville Football Club for the 1985, then coached by
Malcolm Blight. In Woodville's away match against his former team West Torrens at
Thebarton Oval, Muir again retaliated violently to repeated racial attacks. Playing at full-back, Muir was relentlessly hounded by West Torrens supporters in the crowd who, as well as abuse, spat on Muir with one supporter throwing cans and bottles at him. Muir asked his teams support staff to ask the police to eject the offender - nothing happened. At the end of the game, after again being hit by a thrown can, Muir took the matters into his own hands; he jumped the fence and repeatedly punched the offender. The police then intervened - to arrest Muir. Muir was sacked by Woodville as a result and this brought an end to his professional football career. ==Post-football==