Rokus and other streaming boxes generally aren't optimized for live sports. True, there are channels you can install and subscribe to, like NHL, NFL, etc. These are not a good value for a recreational Sunday afternoon type football watcher like myself, but if you're a fervent fan of a particular team, then they may be.
This is why we chose to supplement our Roku boxes with a large antenna. It's installed in our attic and we receive very well three of the major four networks: CBS, NBC, Fox. We do get ABC, but it seems to be somewhat weather-dependent, and we don't watch a lot of ABC anyway. The three networks provide plenty of Saturday afternoon college and Sunday afternoon professional football games, and it's free after the initial antenna equipment purchase. This works for us.
Are you in an area where you can receive good over-the-air reception, and are the Rangers games televised on a broadcast network?