More precise classification: past participle functioning as adjective.
Translations
The sidelined player watched the game from the bench.
Отстранённый игрок наблюдал за игрой с скамейки.
She felt sidelined during the meeting as no one asked for her opinion.
Она чувствовала себя игнорируемой на встрече, так как никто не спрашивал её мнение.
Definitions
Removed from the center of activity or attention; marginalized. After the merger, many long-time employees felt sidelined.
Temporarily unable to participate in an activity, especially due to injury or other circumstances. The star striker remained sidelined for two weeks with an ankle sprain.