Nonparticipant (noun)

1. A person who does not take part in a particular activity or event.
2. An observer who is not actively involved in a situation or process.

Origin:

From non- + participant.

Examples:

1. The nonparticipants sat on the sidelines, watching the game but not playing.
2. As a nonparticipant in the discussion, he preferred to listen and take notes rather than join in.
3. The nonparticipants were not required to attend the meeting, but were welcome to observe if they wanted.
4. She chose to be a nonparticipant in the political process, feeling that her vote would not make a difference.
5. The nonparticipants were content to let others take the lead and make the decisions.