Disclaimer: I work in HFT<p>The article uses the term &quot;front-running&quot; incorrectly. Front-running is where a firm places their own trades ahead of trades they&#x27;re placing for a client, to capitalize on the price movement that client order might generate. This is illegal.<p>What the market makers in the article are doing isn&#x27;t front-running. It&#x27;s just being smart with their orders.<p>And that&#x27;s generally why HFTs cancel orders- they&#x27;re reacting to market conditions that exist on the span of microseconds and will want to change their market positions very quickly- including canceling orders that they no longer think are suitable.