[noway421]

Would it be just one rogue order filled? Not sure how after-hours tracking works, but I assume that it won't have a very deep order book, so it would be relatively easy to manipulate it. Given that BRK.A has the highest share price among any stocks, that order book would be even smaller.

[shmoogy]

It was 4 shares: https://www.nasdaq.com/market-activity/stocks/brk.a/after-ho...

Likely one person that placed a market order

[skzv]

I don't think you can place market orders after hours.

It could have been a deliberate limit order to avoid a margin call by raising the mark-to-market value of an account.

[cbhl]

That sounds like an expensive mistake -- BRK.B doesn't show anywhere near the same price movements.

One does not simply place a market order during after hours trading...

[sp332]

https://www.google.com/finance/quote/BRK.A:NYSE shows a volume of 1 single share at that time.