Depends on your setup. What device is your MLB app on? What Sonos devices do you have?

Are you using an Android or iOS Phone? With iOS you can use Airplay to play to your speakers.

With a Move, they could use Bluetooth, too. But they’ve not responded with any answers, so we’re stuck not knowing hoe to assist them. 

More detail please on the option to bounce MLB.com on iphone to my Play 1 speaker using Airplay? Have never used Airplay. Thanks!

Unfortunately, it can’t be done with a PLAY:1, which is why I asked what devices the OP had. Newer Sonos speakers are able to be the target of an AirPlay 2 signal, and then when grouped with the PLAY:1, you get the content. This is what I do sometimes with TuneIn premium (baseball).