Alliteration helps make the poem's language colorful and robust, evoking the passion of sports and the noise of sports fans.
In the opening two stanzas, the speaker illustrates the fanaticism of Australian rules football supporters by describing how they treat their newborn children. Both the children and their "cots" (cribs) are wrapped in the colors of the local team. The poem presents the babies' wailing as an early attempt at "barracking"—that is, shouting and screaming at the team from the sidelines. Alliteration adds intensity or insistency to the opening lines, capturing the fans' rowdiness and obsession:
When children are born in Victoria
they are wrapped in club-colours, laid in beribboned cots,
having already begun a lifetime’s barracking.
Those bold /c/ and /b/ sounds help capture the gaudiness of the crib decorations and the volume of the babies' cries (which recalls the volume of the stadium on match day!). The second stanza dials this effect up even further, unleashing a run of percussive consonant sounds:
Carn, they cry, Carn… feebly at first
while parents playfully tussle with them
for possession of a rusk: Ah, he’s a little Tiger! (And they are… )
Try saying these lines out loud and notice how muscular and dense they are. This sound ties in with the description of a "tussle" between parents and kids for "possession of a rusk," a kind of proxy competition that mirrors the game of Australian rules football.
The poem frequently comes back to plosive /p/ sounds, as in lines 16, 25, and 32 ("Hot pies and potato crisps they will eat," "That passion persisting," "the past to replenish continually the present"). These sounds pack a powerful punch, evoking the intensity of the fans' devotion to their team. Similarly, in line 32, the poem repackages line 4:
[...] the elderly still
loyally crying Carn... Carn... (if feebly) unto the very end,
This alliteration draws a link between the young fans and the elderly, implying a lifetime of passion for one's team. It suggests the continuity of the life-cycle from birth through old age—unified, of course, by the maddening hope that the team will do well.