General comments/chat, page-14888

If it’s a completed trade the simple answer is that it is both – there has to be both as buyer and a seller for each transaction. Each line in the course of sales data shows one buyer matched with one seller. Lines either side of that with the same timestamp may be part of a bigger buy OR sell order.

If the question is who initiated the trade, you can’t be 100% sure from looking at old data but the direction of change in price from the previous trade should give you a clue. If the price is higher than the previous trade the buyer initiated it as they accepted the seller’s price. If it’s lower, a seller has sold into the bid (which appears to be the case in this example).

Spend some time looking at the course of sales data and the bid/ask spread during trading hours and it should be easy enough to pick up.