。
I walked against the crowd.
Literal
I [topic-は] everyone [against-に] defying walked.
みんなに逆らって ('going against everyone') — 逆らう (さからう, 'to go against, defy') takes に for the thing defied. て-form links to 歩いた ('walked'). Could mean physically walking against a flow of people or metaphorically going against the group.