What does the cryptic crossword clue "Short of time, they run about in stadia (10)" mean?

The wordplay uses an anagram. anagram of HEY (synonym="HEY") + GROUNDS (synonym="GROUNDS") = GREYHOUNDS The answer is GREYHOUNDS.

Short of time, they run about in stadia (10)

Guardian Cryptic #26288 | 12 Down | 2014-06-17 flower