Reminds me of “step function” from mathematics, which represents an instantaneous change in value.
I would take step change to mean an instantaneous (or very rapid), rather than gradual, change. The use in this BBC Sport article on gymnastics is a play on words.
Some general examples:
A step change for biodiversity knowledge
“The hopes are high for IPBES to become an authoritative global mechanism recognized by scientists and policy makers alike to pull together dispersed information, syntheses and analyses on biodiversity and ecosystems. By building on existing processes and initiatives, and only creating new ones as a last resort in case of glaring gaps, the intention is that decisions and research investment will be more efficient,” writes Julia Marton-Lefèvre, IUCN Director General.
A step change for Britain’s buses: Maximising the economic, social and environmental potentia
* Dramatic or radical change in one fell swoop
* Radical alteration in the business
* Gets it over with quickly
* May require some coercion
Edit: fixed some formatting