Anyway, so far it seems like the top 10 or so are
Football
Horse racing
Rugby Union
Cricket
Rugby League
Greyhounds !!
Motorsports......
Tennis
Golf
Ice Hockey
Equestrian (?)
This from 2015 about the main sporting events that year
The top-10 for 2016 are as follows:
Wimbledon — 494,000
Formula 1 (Silverstone) — 327,000
Royal Ascot — 295,000
Cheltenham Festival — 261,000
ATP World Tour Finals — 252,000
The Open [golf] — 173,000
Badminton Horse Trials — 160,000
MotoGP (Silverstone) — 156,000
Burghley Horse Trials — 155,000
Epsom Derby Festival — 154,000
Think both Wimbledon and Silverstone have upped that number in the past couple of years