There is no specific statutory definition of sports betting, but the definition of betting in section 9 of the Gambling Act 2005 would normally apply. Sports betting is simply betting as defined in s9 where the event or process concerned is a sporting event of some kind.
For “gaming”, the relevant definition is in section 6—gaming means playing a game of chance for a prize. The terms “game of chance” and “prize” are further defined in s6(1), which also contains other interpretation provisions.