He returned to Australia and Sydney's Northern Beaches in 1956, joining the Manly-Warringah Sea Eagles who played in the New South Wales Rugby League Premiership and became the cornerstone of their forward pack in the late 1950s.
Ever an aggressive front-row forward, Mossop played in the Manly sides that lost to the St George Dragons in grand finals in 1957 and 1959.
Mossop later recalled how after both he and Bath had left the league judiciary the following week, that they got talking and both got a laugh about being told off like naughty school boys.
Mossop first appeared on air in 1964 and called his first game in 1965, only four years after former player Ray Stehr had carried out the first ever commercial telecast on Channel 9 in 1961.
From the early 1970s till 1990 on Sydney channels Seven and then Ten he was the voice of rugby league and the pre-eminent TV match broadcast caller.
His match commentaries and indeed his other forays into the public domain were often filled with tautological descriptors that in eastern state Australian vernacular became known as "Mossopisms":[6][7] These mistakes also led to his nickname, "Rox Messup".
[8] He also recorded such classics as: The perceived parochialism towards Manly - and a gruff style that bordered on arrogance - often alienated him with league supporters, so much so that he was once famously hit in the side of the head with a piece of fruit thrown at him while giving a live post-match summary.
Never one to hold back his comments, when describing the Australians 34-4 demolition of Great Britain in the second test at Elland Road in Leeds during the undefeated 1986 tour, Mossop said as Brett Kenny crossed for the Kangaroos 6th try (pushing the score at that stage to 32-0) "Australia carved them up.
[11] From 1991 to 1995, he was a regular panel member on Andrew Denton's sport-themed comedy talk show, Live and Sweaty, on the ABC alongside others including actor Lex "The Swine" Marinos, former Australian rules footballer Peter "Crackers" Keenan, Karen Tighe, Debbie "Skull of Rust" Spillane and Elle McFeast (Libbi Gorr).
He attended Manly Boys High School, leaving in 1943 to become initially an apprentice fitter and turner, and later a sales representative for a variety of businesses prior to his career in television.
In 1976, Mossop made a citizen's arrest of a nudist at Balgowlah Beach later stating "I don't need the male genitalia rammed down my throat".