Jaguars is a good team name. It begins with the letter j.
St Johnstone, the Super J's (copyright Soccer AM)
The team is St. Johnstone from Perth. The letter is J.
Only one team in the UK even has a J in it's name. St Johnstone. This does not begin with a J, however.
The New York Jets
I don't think there is an English team with a J in the name, however, there is a british team in Scotland, called st johnstone