This question/teaser has been buzzin around work for a few weeks now,but nobody has ben able to crack it

Some smart ass help please


"What enters the field of play in a football match at half-time, but doesn't leave until the match is over? If it's a Saturday match it leaves after the game, but if it's a mid-week game it remains until the next day... and it only happens in the English Premiership, not in Scotland or the lower divisions..."

Cheers. Dave