Matt LeBlanc is rooting <em><u>for</u></em> the other team.
Explanation:
Prepositions tell the position of the noun or pronoun with respect to the other words in the sentence. It tells the relation of the different words or phrases in the sentence.
In the given sentence <em>"Matt LeBlanc is rooting for the other team"</em>, the preposition is "for". It tells the relation of which team or who Matt Leblanc supports.
