1 Corinthians 9:26

I therefore run, as not uncertainly; so fight I as not beating the air.

This indicates that "The whole of this chapter has been a vindication of Paul's self-denial,"[21] the object of it being the persuasion of the Corinthian boasters of their "liberty" to follow Paul's example by denying themselves all indulgence at the expense of the faith of their weaker brethren.

Beating the air ... is a reference to boxers who missed with their punches and so lost the fight. "Uncertainly ..." has reference to contestants in a race who, through lack of training, wobbled to defeat, not victory.