This is actually going back a long time; I think to about 1985. At that time I was running a game of RuneQuest , set in Glorantha, which had already been running a couple of years.
I had heaps of RQ material, and lately the group had been messing around with various missions and stuff in the Troll lands. Gloranthan cultures are marvellously detailed and none more so than the Trolls, or Uz. One little cultural detail is the game of trollball, in which the ball is a live trollkin and the referees are giants. Otherwise more or less like American football.
(I see you can now actually purchase the game as a boardgame from Chaosium
The session divided into several parts. The first part was straight in-character interaction with the troll NPCs. They had previously met these NPCs out in the wild and established friendly relations. There was a big trollball match coming up and this village/town was hosting it.
The second part was a scratch match of trollball that some trolls invited the PCs to play in. For this we busted out the hex grid map from Trollpak and did tactical movement (also combat, because weapons are allowed in trollball). The best part was when one of the giants refereeing literally booted one of our PCs out of the game (there were rules for this, e.g. how far a character of given size would be punted with a kick).
The third part of the game was the most illuminating part for me. The whole game had been building up to the big match, and I had been worrying about how to present it all game. We'd even picked up a couple of spectators, friends of the host who'd dropped by for something and ended up getting drawn into the game.
I didn't know whether to set the board up again or what. Should I get the group to play NPCs? BUt the scratch match had been fun and I felt that setting up the hex grid again was just going to be anticlimactic.
In the moment, I just winged it. I started describing the game, and rolling the dice. I had done some theatre; I looked at my audience and I had them. For several minutes I simply rolled dice and talked – leaving the PCs out of it entirely. I built the tension with an almost tied game; I released it with a spectacular goal with seconds to go. "YAY!!!" all round the table, even from the visitors. Buzzy feeling all round.
I was a bit stunned. I had entertained the table by myself. This wasn't roleplaying, it was theatre. I sat there basking in the effect and feeling like something had gone vaguely wrong.