Olympic swimmer Danielle Hill, who trains at Larne Leisure Centre, described the attack as not just violence, but "racism in its rawest and most dangerous form".
Hill, who takes a weekly group swimming session, arrived at the centre at 19:00 BST yesterday.
"This is our club night, so one of the busiest nights of the week," she told BBC News NI.
After cancelling her session, when she saw masked men approaching the centre, Hill told people to evacuate.
"I lay awake last night, when there is kids involved it's upsetting and it shouldn't be happening," she said.
She hopes that the children who were present will not be afraid to come back to the leisure centre.
Hill represented Ireland at the 2020 and 2024 Summer Olympics.
Lyndsey Telford describes being on the ground during violence disorder in Ballymena
What is happening in Ballymena?
On an extra episode of BBC News NI's The State of Us podcast, Tara and Declan speak to reporter Lyndsey Telford who has been on the ground during the violence and disorder in Northern Ireland.
Leisure centre was set on fire in third night of violence in Northern Ireland
The worst of last night's disorder was in Ballymena, but unrest also spread to other towns.
In Larne, about 20 miles (30km) from Ballymena, masked youths attacked a leisure centre and set it on fire.
The centre had been providing emergency shelter for families following the clashes earlier this week.
Police left the area after masked young people threw objects at vehicles, but later officers in riot gear returned to the scene.
A crowd of about 50 people watched a dozen or so individuals target the centre.
Fire damage was contained mainly to the front reception but there was extensive smoke damage, the fire service said.
In a statement, Mid and East Antrim Borough Council said the families placed at the centre had all been "safely relocated" and were no longer using the centre.
Earlier today, a judge warned that anyone involving themselves in the ongoing “despicable” rioting “will be dealt with robustly".
Speaking as he remanded four teenagers into custody, District Judge Nigel Broderick said that “where there is credible and reliable evidence” against anyone arrested in the ongoing disorder, “there is a high likelihood they will be refused bail and if convicted, they will face lengthy sentence.”
The judge issued the warning at Ballymena Magistrates Court where the teenagers appeared in the dock charged with riot.
Image source, Reuters9 June: Two teenage boys appear in court charged with an alleged sexual assault of a girl in the Ballymena. They spoke through a Romanian interpreter to confirm their names and ages - their solicitor said they would be denying the charges.
9 June evening: Hundreds held a peaceful protest related to the court case but violence later broke out when people threw petrol bombs, bricks and fireworks at police, and damaged properties. Police called it "racist thuggery", targeting ethnic minorities and law enforcement.
10 June: During a second night of riots, police fired baton rounds and used a water cannon to disperse protesters in Ballymena as cars were set on fire and windows of several houses were smashed. Police also dealt with incidents in Newtownabbey, Carrickfergus in County Antrim and north Belfast - 32 officers were injured and six people arrested over the two nights.
11 June: Violence spread to other towns like Larne - about 20 miles (30km) from Ballymena - where masked youths attacked a leisure centre and set it on fire. The town was providing emergency shelter for families following the clashes in Ballymena.
Yelena, who is Filipino and moved to Ballymena last year, tells the BBC: “To feel safe I put a Union Jack flag outside my window, since then the building hasn’t been attacked.”
She says she had considered putting up a Filipino flag but her local friends told her she might still be attacked.
She didn't expect trouble to start where she lives, but it escalated from a small gathering to setting bonfires, throwing petrol bombs, and throwing stones, bricks and glass bottles at her windows.
“I'm doing OK but still a bit traumatised,” she says.
“I don't want to leave Ballymena, I just want everyone to be educated on migrants - not all those here are illegal.
“I want to go back to work and have peaceful nights.”
Image source, ReutersPolice aim a water cannon at demonstrators as riots continued in Ballymena on Wednesday
The violence in parts of Northern Ireland is described as being racially-motivated by officials, with police calling it "racist thuggery targeted at ethnic minorities and police officers".
It started on Monday 9 June, after two 14-year-old boys appeared in court after an alleged serious sexual assault on a teenage girl in Ballymena, County Antrim, on Saturday 7 June.
The teenagers, who confirmed their names and ages through a Romanian interpreter, are charged with attempted oral rape, which they deny.
That evening, a peaceful protest was held when hundreds marched close to the town centre, before things turned violent and youths with their faces covered attacked police and a number of houses.
The first two nights of violence saw 32 police officers injured after being attacked with fireworks, bottles and bricks, and six arrested. Videos on social media have shown houses being attacked with families still inside - signs outlining residents' nationalities have been put up on some doors.
Violence spread to the nearby town of Larne - when masked youths attacked a leisure centre and set it on fire - which had been sheltering families caught up in the disorder earlier in the week.
Welcome to our live coverage. Chief Constable Jon Boutcher from the Police Service of Northern Ireland (PSNI) will shortly give an update after a third night of violence in parts of Northern Ireland.
The riots started on Monday, after a planned peaceful protest in response to an alleged serious sexual assault in Ballymena, in County Antrim on Saturday evening.
On Monday, two teenage boys appeared in court and confirmed their names and ages through a Romanian interpreter. The two 14-year-olds denied the charges against them.
Since then, violence has spread to other towns, 32 police officers have been injured and authorities have struggled to keep the peace.
You can follow the police press conference at 15:30 BST by pressing watch live at the top of this page, and we'll bring you text updates here.