He made his debut for Carlton on 7 May 1921, playing on the half-forward flank, against Richmond, at the Punt Road ground.

At the annual meeting of the Stratford club last January it was decided to secure a coach for the year 1925, and after much discussion Alex Duncan, of Carlton, was elected.

He is classed as one of the greatest footballers Gippsland has ever seen; his kicking, which covers long distances, and his aerial work being a feature of every match.

Duncan (Stratford's coach and captain) marked his first appearance in Gippsland football… by winning the toss, playing a good game, kicking five goals and leading his side to victory [over Rosedale, 13.14 (92) to 9.7 (61)]".

[7] Moved from the forward line to centre half-back, he played his first return game for Carlton, against Melbourne at Princes Park on 8 May 1926 (round two).

The encounter between Carlton and Collingwood Football Club at Victoria Park on Saturday, 25 June 1927, in which a strong Carlton team outmuscled, outplayed, and (coming from behind) beat a champion Collingwood team playing at its peak, is one of the most famous encounters in the game's history; and is remembered as "Duncan's Match".

[9] According to The Age, "Duncan's meteoric marking and wonderfully dashing defence was the most sparkling individual performance of the season".

[10] According to The Argus, "Duncan his played many fine games for Carlton, and has also been a tower of strength in interstate teams, but he has never been seen to better advantage.

[20] The Havelock club withdrew from the competition before the start of the 1937 season, due to its difficulty in attracting sufficient suitable players.

[22] Despite coming a close equal second with Melbourne's Dick Taylor to Collingwood's Syd Coventry in the 1927 Brownlow Medal, having been declared best on the ground in six matches, compared with Coventry's seven (at that stage only one vote was given to one player in each game),[23] Duncan had quite a history of rough play.

During the particularly torrid match against Collingwood at Princes Park on 29 July 1922, which Carlton won, Duncan scored three goals despite being knocked out on two separate occasions.

[24] In a torrid, low-scoring match at a windswept Princes Park on 21 June 1924, against Richmond, which Richmond won 5.8 (38) to 3.10 (38), Duncan was reported three times: for elbowing Reuben Reid, for kicking George Rudolph whilst he was on the ground, and for making an offensive gesture towards Boundary Umpire Johnson.

In giving his evidence, Duncan stated that after he had taken the mark he was kicked on the leg and, without using any bad language, he had said "Cut it out Wilson, you have been at it all day."

Duncan protested that Sale had only complained to retaliate for Wood having been reported by the field umpire.

Duncan pleaded guilty; but argued in his own defence that he had not heard the umpire's whistle blow, and had pushed Dyball to delay the play.