Pompey refers to Portsmouth FC and it is this team that has the largest Pompey supporters club. the club was bought by the Pompey Supporters Trust in 2013.
Real Madrid C.F.
It is Manchester United.
Grobari, who are organized supporters of the Serbian football team called the Partizan Belgrade, avidly support their team. Their motto is "The others are cheered, but Partizan is loved.
i hopeing you mean soccer. if so, Manchester untied are said to have the largest amount of supporters in the world (only about 1% of them from Manchester, glory supporters, cough cough) so if you mean that by the biggest, then them. if you mean the most players, biggest stadium or the average of all that and more factors, well, i just don't know about that, sorry
The football team with the largest squad is either Real Madrid or Manchester United.