Sub-only (submission only) is a competition format where only submissions end a match. There are no points, no advantages, and no judge decisions. If time runs out without a submission, the match goes to overtime — typically sudden-death overtime starting from a predetermined position, or a coin flip for starting position in extended overtime.
Sub-only events like Polaris, Quintet, and ADCC encourage athletes to hunt finishes rather than accumulate points by achieving and holding dominant positions. The ruleset tends to produce more dynamic, aggressive matches with higher submission rates than the standard points format.
Sub-only is common in no-gi competition but exists in gi formats too. Heel hooks and many leg locks restricted in IBJJF are often legal in sub-only events, which changes the strategic landscape significantly.