Exactly How a Run Ends

Not when the stack looks full, but when a new piece has nowhere to spawn.

The run ends when a new piece cannot be placed at its spawn position because something is already there. That is the whole condition.

Not what people assume

It is not "the stack reached the top line". You can have blocks in the topmost visible row and keep playing indefinitely, as long as the spawn area stays clear. Plenty of good runs involve a stack that spends time uncomfortably high and comes back down.

The failure is specifically about spawn space.

Where pieces spawn

Pieces appear near the top of the well, horizontally centred. TETERI keeps a small buffer of hidden rows above the visible field so rotations near the ceiling have somewhere to kick into, which is why a piece can occasionally rotate upward when there is no visible room.

The check is simple: place the new piece at its spawn cells. If any of them are occupied, the run is over.

The garbage variant

In versus modes there is a second way out. Incoming garbage pushes your entire stack upward. If that push would force blocks out through the top of the field, you are eliminated, even if you were not about to top out on your own.

This is why an incoming garbage meter is genuinely alarming rather than merely inconvenient. Six queued rows against a stack that is already twelve high is a loss, and no placement you make will change that. Only clearing lines to cancel it will.

Why it feels sudden

Because the condition is checked at spawn, the end arrives between pieces rather than during one. You place a piece, it locks, and the next one simply cannot appear. There is no warning frame.

That is a fair design, since the information was all on screen, but it does mean you rarely feel the last moment coming. This is why the danger line matters: TETERI marks the height at which you are running out of room, so the warning is spatial rather than temporal.

The practical lesson

Keep the middle columns low. Pieces spawn in the centre, so a stack that is tall at the edges and low in the middle can survive far longer than one of the same total height with a central spike.