What does the cryptic crossword clue "Game turned round: possibly I initially underestimated Man U (7)" mean?

The definition is "U". The wordplay uses an anagram. UR (synonym="UR") + ANIUM (synonym="ANIUM") = URANIUM; definition: "U" The answer is URANIUM.

Game turned round: possibly I initially underestimated Man U (7)

Guardian Cryptic #29274 | 22 Across | 2024-01-09 flower