Former Premier League referee Mike Dean says he used to set himself mini-challenges during matches "as a laugh".
Appearing on Jamie Vardy's podcast, Dean said he would see how long he could go without blowing his whistle, or stay inside the centre circle.
"We used to say 'we'll kick off now. Right, see how long we can go without blowing a whistle'," Dean said.
"I've done that a few times in the Premier League, before VAR obviously - went 20, 25 minutes without blowing a whistle.
"I used to do another thing. I used to stand in the centre circle - see how long I could stay in the centre circle before I had to leave.

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