The Pompey die-hard received the punishment after a 2-0 home pre-season defeat to Coventry City.
A video captured the 59-year-old rubbing his bottom towards away supporters.
Portsmouth Traffic: M27 between junctions 11 and 12 closed throughout August amid footbridge repairs with A27 diversion in place
Thunderstorms in Portsmouth yellow weather warning: The Met Office forecast for the next three days in city, Fareham, Gosport, Havant and Waterlooville and Hampshire
‘I watched ten years of my children’s lives go up in flames': 'Traumatised' Paulsgrove mum of five launches fundraiser to find family new home after they 'lost everything' in bedroom fire
Detectives 'file' investigation into woman's abduction in Rowner after failing to find a suspect
'Manipulative' paedophile who went to Farnborough Railway Station with cans of Strongbow cider to meet girl, who he asked to travel 100 miles, busted by undercover police officer
He said he started making the lewd gestures after being moved by stewards towards the Milton End due to noise complaints from fellow supporters – receiving verbal abuse from opposition fans.
‘I did those things at the game after extreme provocation,’ Mr Westwood said.
‘With my profile, I’m having hundreds of them swearing at me and calling me a paedophile.
‘I’m taking all this abuse, so I do some light-hearted banter back by doing a moon.
‘It was done in humour, and my friends who have seen the video thought it was funny.’
He said the stewards did not understand the historical problems between Portsmouth and Coventry fans, citing a riot in 2000.
Mr Westwood described a meeting with the club as something out of the Soviet Union.
‘It was a kangaroo court,’ he added, ‘It’s cancel culture.’
‘I feel sorry for the club because they’re under pressure to do something because of keyboard warriors and this political correctness-driven world.
‘You won’t be able to fart in a ground soon without offend someone.’
Although accepting his ban, Mr Westwood said Portsmouth’s laddish culture created the atmosphere, which led to him chanting: ‘Pompey is a geezer’s club’.
‘You need a bit of raucousness, and if you take that out of the game, you’ll kill it,’ he added.
‘You’ve seen worse on TV. If that was Kim Kardashian twerking, it would have been fine.
‘I’m just gonna carry on being me, loud and proud, singing Pompey songs, and maybe some wokey PC ones.
But Mr Westwood has been accused of making misogynistic comments at matches, which he denies.
Pompey has partnered with Her Game Too, a non-profit organisation campaigning against sexism in football.
Fan and ambassador, Rebecca Eleanor, said the video of Mr Westwood was ‘disgusting’ and ‘made her skin crawl’.
She said: ‘We know when you go to a football game that it’s not the atmosphere of a theatre.
‘Since it’s a pre-season friendly, you’ll have families bringing their kids, maybe for the first time.
‘If i went to that game when I was first going to Pompey, as an 11-year-old with my dad, he would not have brought me back.’
Ms Eleanor said she saw Mr Westwood making jokes about the ban in a Sheffield pub, and said chants about geezer’s could be problematic if it includes sexist remarks.
She said Fratton Park’s atmosphere is due to passionate fans and none-stop singing, not laddish culture.
‘Women laugh and cringe when we heard things he sang, but it is not acceptable anymore,’ she said.
‘From what I saw in the Sheffield pub, he seems to not understand what he has done.
‘Pompey can’t partner with Her Game Too, and say we’re against sexism in football, and let him and those around him make people feel uncomfortable.’
Mr Westwood’s match ban will be lifted after today’s match.
A Portsmouth FC spokesman said the club ‘won’t comment on individual cases, but will always investigate any complaints made concerning inappropriate supporter behaviour’ and would take ‘appropriate action’.