Do you know any IoT sensor for speed detection of a human and sending it to a mobile application?
In other words, I am looking for a very small IoT sensor that sends the speed data of players of a sports team to a mobile application.
I am not sure if your budget allows it, but I know Garmin has a few APIs for collecting data from their fitness trackers, like speed. They call it Flexible and Interoperable Data Transfer Protocol or "FIT". The only downside is that the data must be collected from their Garmin Connect site, not direct from device. It also has a pretty hefty one time fee to access the data for your application. But depending on your budget and audience, perhaps it is worth looking in to! Hope this helps.
You can check out the SDK for FIT here to see if it is worth your time: https://www.thisisant.com/resources/fit
More Info: https://developer.garmin.com/garmin-connect-api/sample-data/