The problem with Brantley and Marty and to a lesser extent Thom Brennaman, is that the vitriol that they spew against certain players, like Dunn and Encarnacion, could lead to those players deciding to leave. Dunn has said multiple times that the Brennamans and Brantley bother his mother so much that she won't and cannot listen or watch whenever they are doing the commentary.

From the Red Reporter, some things that Marty Brennaman has said about Dunn:

He is going to make $10 million this year. I get tired of people saying he hits 40 home runs and drives in 100 runs. Wonderful. This is a guy who should hit 50 plus home runs and should drive in 130 runs or more every single year. And he can't do it because he leads the world in strikeouts. I think he was overweight last year. He walks to his position. He walks off the field. You see no energy whatsoever and that disappoints the heck out of me.
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Adam Dunn, even though he struck out 195 times last year, he walked over 100 times last year, so he has a great eye. I'm thrilled to death that he walks that much, but he's not paid to do that. The most shocking stat of my 31-year career was last year, in 568 at-bats, he did not have one sacrifice fly.

And then there is what Brantley said about Todd Coffey:

Brennaman: "Well, it’s hard to understand how a guy can come in when a team is behind and pitch so well, and then come in to try to protect a lead ... There’s ball three. It’s just truly amazing."

Brantley: "You can’t throw the ball with your right hand if your right hand is on your throat. You can’t do both.