[gumby]

In addition to the choices already offered (just give it away or sell it like any conventional piece of software): I would favor your choice of seeing the results.

But don't encrypt the results -- what's the incentive to use the app then? Instead provide value to any user (it collects and saves the results locally), but for a subscription the data collector could upload the results.

Then you have a choice: does the event holder or the competitor (or both) pay to see the results? The fact that you collect them means competitors who compete in different events can see all their results, view leaderboards and the like. You could pretty well automate all that so your involvement would be minimal. I don't understand your domain but without prior knowledge I would think it would be easier to charge the contest holder.

Your model might be something like Strava.