When Teemo Strategist's ability triggers during a showdown he's defending, can Nocturne be played into that same battlefield?

Ruling: Yes, Nocturne can be played into the battlefield Teemo is defending during a showdown. Card text supersedes normal timing restrictions - while units normally cannot be played during showdowns (which are in a "showdown closed" state), Nocturne's specific triggered ability allows him to be played when revealed from the deck, and he can be played into any battlefield his controller controls (including one they're defending).

Sequence:

• Showdown begins at the battlefield Teemo Strategist controls
• Teemo's defend trigger goes on the chain
• When Teemo's ability reveals Nocturne from the deck, Nocturne's triggered ability allows him to be played
• Nocturne can be played into any battlefield his controller controls, including the battlefield being defended

Nuances:

• Normal units cannot be played during showdowns because the game state is "showdown closed" (not neutral open)
• Units with "action" or "reaction" tags have different timing exceptions than Nocturne's specific triggered ability
• The restriction isn't specifically about playing units into battlefields you're defending - it's about the game state during showdowns
• Card text supersedes normal rules when there's a contradiction