I presume you mean illegal pirated feeds when you say free?
My understanding is that many people use the Kodi app. This is a sort of general media player app that uses things called "add ons" to access repositories that host the sort of thing you're looking for.
Kodi is widely available and installable directly on many devices, for example you can add the Kodi app to many Smart TV - you don't necessarily need a Fire Stick.
Some gadgets make it a bit farty to add Kodi (or any general apps) onto them. For these sort of gadgets (which may include Fire Sticks) the process of adding these additional apps is often called something like Side Loading or Jail Breaking. These are terms to make the fairly simple process of adding apps sound sexy and illicit.
You have two options going forward: Google "adding Kodi to Firestick" and "best Kodi Sports add-ons" and sort yourself out OR, ask a 12 year old son/nephew to sort it all out for you.... it'll take them 5 mins tops.
I think there are other threads about it if you search "Kodi" on here.