Muscat was branded a “lowlife” and a “nobody” by ex-England striker Ian Wright, then of Nottingham Forest, in September 1999. Wright claimed he was about to shoot when he heard Dougie Freedman, Forest's other striker, shout "leave it". Wright stepped over the ball to allow Freedman to hit it, but instead Muscat (who had, according to Wright, merely impersonated Freedman) appeared to clear the ball.[11]

Muscat was dubbed the "most hated man in football" by then Birmingham City player Martin Grainger in 2000.[12] He seriously injured both Craig Bellamy and Christophe Dugarry, the latter in a friendly international between Australia and France in 2001 with a sliding tackle from behind.[12] The French manager Roger Lemerre dubbed the tackle "an act of brutality".[12][13] There was speculation that Muscat’s temperament was the reason he was never selected for inclusion in an Old Firm encounter during the season he was at Rangers.[14]

In 2004, a lawsuit on Muscat brought by former Charlton Athletic player Matty Holmes resulted in a settlement of £250,000 plus costs in favour of Holmes, bringing the estimated settlement to around £750,000. Holmes had to have four operations on his leg following a tackle by Muscat in 1998, and there were initial fears that his leg might have to be amputated. The claim was settled at the High Court without any admission of liability.[15][16] In a League Cup tie while at Millwall, he grabbed the throat of Liverpool striker Milan Baros.[17] Also in 2004, Iwan Roberts admitted he deliberately stamped on Muscat in a match against Norwich City in revenge for his attempt to injure Craig Bellamy in 1999. Roberts was subsequently fined and suspended by the Football Association for his comments.[18][19]

In December 2005, he was the first A-League player to appear before a FFA disciplinary hearing and was subsequently suspended for two matches for "violent conduct".[20] At an A-league game in October 2006 Muscat clashed with then Adelaide United coach John Kosmina, knocking Kosmina from his chair while retrieving the ball. Kosmina responded by grabbing Muscat by the throat, an action for which Kosmina was suspended for four matches.[21][22]

Muscat's dominant personality and aggressive style has equally won him admirers and detractors in the A-League, with former England international Terry Butcher stating "Every manager in the A-League would love to have Kevin, and I'm no exception".[23]

In October 2010, Aston Villa winger Ashley Young recalled he was threatened by Muscat during his first professional match as an 18 year old. "Kevin Muscat said he would break my legs if I went past him," said Young. Their meeting occurred as they were warming up for an encounter between Watford F.C. and Millwall back in September 2003, but Muscat was sent off before Young came on as substitute for Watford.[24]

In January 2011, Muscat was suspended for eight matches following a tackle on Melbourne Heart player Adrian Zahra in an A-league fixture.[25]