Selling a call short is an uncovered or naked position aiming to collect premium from the sale of the option in expectation of neutral to bearish price action.
If the underlying stock is already owned, then selling a call against that long stock is known as a covered call.
Naked calls involve upside risk in the stock. For example, if a call is sold in XYZ for $0.40 at the $25 strike, and XYZ is trading at $26 by expiration, the call has moved ITM. The trader has the choice to either buy back the short option (for a loss since the option would be trading around $1), or get assigned a short stock position in XYZ at $25. The premium collected from selling the call is kept, which effectively improves the basis for the short stock position if assigned. In this case, the trader would be short the stock with a basis of $25.40 ($25 strike price plus $0.40 premium collected from call sale).
Short calls have a negative delta, so they are a bearish position unless paired with long stock.
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