。
The defenders put up strong resistance.
Literal
Defenders [topic-は] strong resistance [object-を] showed.
防衛者達 ('defenders') uses 者 ('person') + 達 (plural suffix) attached to 防衛 ('defense'). 抵抗を見せる literally 'to show resistance' = 'to put up resistance.' A military/conflict description. 見せる ('to show') used metaphorically for demonstrating a quality.