I put root in quotations because I'm not sure if it's used outside of North America or not. Anyway it means a team you cheer for. Here are mine:
Calgary Flames/Detroit Red Wings (NHL): some people treat cheering for two teams like polygamy, but this an exception I can assure you. I grew up with a family of Red Wings fans so I have a soft spot for them, but I was also a Flames fan because their logo was a Flaming C (as a kid I thought it was cool because my first name starts with a C).
Detroit Tigers (MLB): For some reason when I was a kid I liked the White Sox, but now I stick with the Detroit team.
Detroit Lions (NFL): For some reason when I was a kid I liked the Dolphins, but now I stick with the Detroit team.
Detroit Pistons (NBA): ...
Middlesbrough (Club football): When I first started following the sport closely in 2011, I watched a documentary and Middlesbrough won me over. Unfortunately they've only been in the Premier League one season since then. Maybe of Detroit got an MLS team they would be my main allegiance.
Richmond Tigers (AFL): I got into Australian rules football last year right before the season started and picked Richmond partly because they hadn't won anything since the 1980s. But then Richmond were champions last year.