Hot and bothered. Wellington Phoenix and Adelaide United players before kickoff in Adelaide with 38C temperatures.

How hot is too hot for football?

If you ask the Wellington Phoenix, an ambient temperature of 39 degrees Celsius in Adelaide on Sunday for their 2-2 draw against Adelaide United, in which one of their players vomited at halftime, is too hot.

If you ask Football Federation Australia (FFA), those conditions would not normally have warranted a drinks break under their rules, let alone a shift in kickoff time.

FFA determine the risk of heat-related injury by using the Wet Bulb Globe Temperature (WBGT). That takes in ambient temperature, humidity, cloud cover, solar radiation, wind, shade, and the time of day.

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It read 25.6C at the 4.30pm (local time) kickoff, which can be attributed, in part, to the 11 per cent humidity level.

GETTY "They're absolutely shattered.'' Wellington Phoenix co-coach Chris Greenacre tells media some of his players suffered heatstroke in Adelaide.

The FFA cutoff to move a kickoff time back is 28C. Drinks breaks are normally only allowed when it sits between 26C and 27.9C, but Hyundai A-League boss Greg O'Rourke was in attendance at Coopers Stadium and intervened to ensure drinks breaks every 15 minutes - double the normal number of breaks used in a heat-affected match.

Phoenix stalwart Vince Lia said it was the hottest match he had played in in his 211 games in the league over 12 years, having missed the 40C match against Newcastle in 2009.

FFA erred in not pushing the kickoff time back, he said.

"The Wet Bulb was below what it had to be. They said it wasn't hot enough to be pushed back, which I think is completely wrong because it was boiling out there. How hot does it have to be to have the game pushed back?"

Centre back Ryan Lowry was one to particularly feel the effects of the heat, despite playing his youth football in the normally scorching Western Australia. That may have been more to do with it being his first 90-minute effort since November 12.

Lia cuts a slender 73-kilogram figure and said he was significantly lighter after the game.

"You weigh yourself before and after and everyone lost a minimum of three kilos. I lost 3kg, which is quite a lot, normally I'd lose between one and two."

It was a quiet changing room at halftime despite the team leading 2-1 thanks to goals from Roy Krishna and Tom Doyle. A few players headed to the toilets as co-coaches Des Buckingham and Chris Greenacre tried to deliver a halftime speech.

"Everyone was pretty dazed at halftime," Lia said.

"In the beginning everyone was just getting their breath back and doing what they needed to for the second half.

"Des and Greeny spoke about what we needed to fix and what we needed to keep doing, touching on that it was going to be a battle, it was going to be horrible, but we had to do it. There wasn't much tinkering going on, just making sure we were switched on and ready for the fight in the second half."

Greenacre said after the match that they made a request on Saturday for the kickoff time to be moved back.

"It's about the welfare of the players, that is what matters.

"Supporters will always come to the games and we're concerned of their welfare; the players are the guys out there that are really putting their necks on the line."

An FFA spokesman said in a statement they went above and beyond their normal rules to ensure player welfare.

"All Hyundai A-League matches are played under the FFA Heat Policy, which is an agreed policy that offers a framework to ensure matches are played well within worlds best practice health and safety standards.

"In line with FFA's Heat Policy both clubs were informed throughout the week of the forecast WBGT for Adelaide on Sunday to ensure the players were professionally prepared.

"The WBGT reading before the match on Sunday in Adelaide was 25.6. Despite this, head of Hyundai A-League Greg O'Rourke, who was at the match, consulted both team doctors and it was agreed to insert drinks breaks into the match as a further sign of FFA's interest in player welfare. This was all agreed and acknowledged by both teams."

Greenacre said after the match that some of his players had been suffering from heatstroke, which was refuted by FFA.

"FFA has since been informed by medical staff at the match that no players suffered heatstroke during the match," the spokesman said.

FFA would not have entertained the Phoenix's request for a later kickoff, with all decisions to move kickoff times made from the Wet Bulb reading.

Wellington faded in a stifling second half, with Adelaide grabbing an 80th-minute equaliser.

And it was a costly result for the Phoenix, who would have been fifth had they won - instead, they're seventh.