I bet he hated Sherman.
He did and he wasn't the only one. It got glossed over last year because of BullyGate, but right before Martin left the team it came out that Mike Wallace was furious with how Sherman was using him, and the offense as a whole did not like how Sherman was calling plays or how he was throwing them under the bus.
Now let's get one thing clear, while I was no fan of Sherman the OL really hindered him, but at the same his constant response of "The play was fine, our players just didn't execute" is not the right way to handle things in front of the cameras and microphones especially in the day of social media. Now in a lot of instances it may be true, but compare his attitude to Bill Lazor's where Lazor's response to a failed play is "We need to talk about why the play failed and what we have to do to fix it". Players appreciate that response more than Sherman constantly going "The play not working wasn't my fault"
I also remember Sherman praising Wallace saying he was having a great year (this was early), and when the reporters told Wallace about it he was almost speechless and basically said he was barely involved.
And Wallace was not the only one to bash him. Brian Hartline went on several radio shows as guests and while he was diplomatic, he did not hide his displeasure, agent David Canter continuously bashed Sherman (and Philbin and Ireland) on twitter, and both Darlington and Volin said that Sherman was not a very popular figure with the players or even some of his offensive staff (I guess how he treated both Clay and Egnew that was shown in an episode of Hard Knocks really bugged Dan Campbell)