What does the cryptic crossword clue "Eccentric learns about a London football side (7)" mean?

The definition is "side". The wordplay uses an anagram. anagram of LEARNS + A = ARSENAL; definition: "side" The answer is ARSENAL.

Eccentric learns about a London football side (7)

Daily Mail Cryptic #17025 | 13 Across | 2023-02-02 flower