Over the past decade we have had:
** cricket taking the lead (actually it was an independent television company covering Test cricket for C4 which started the revolution) where umpires can ask for television assistance over run-outs but not yet LBWs or stumpings though the technology is there
** rugby league and rugby union referees can ask for television help for disputed tries
** tennis players can ask the unpire for a ruling on whether shots are in or out; they are allowed 3 requests a set
P.S.
** athletics introduced electronic starting blocks and photo finishes in the 1948 London Olympics
Soccer, the world's favourite sport, languishes behind largely due to its feudal organisation and the lack of vision of Sepp Blatter, its President.
How could television cameras help the referee?
** penalty kicks and doubtful goals - referee could ask to see the video
** the captain of the team could have one "Ask" card per half for a doubtful goal, a sending off offence or a penalty
This should be introduced in time for the new season in August.