Not sure, I was close to where he eventually sent him off. The ref seemed to be explaining things to Crooks as they walked, he certainly got involved after the horror tackle but so did others, particularly Ash Taylor. I think the ref wanted to wait a few moments so the Walsall player was down the tunnel and there could be no afters. I don't see how he got singled out though, I think the ref wanted to even things up.
Taylor was closest to the incident, was rightly enraged and shoved Bakayoko but before the ref got close. Crooks did no more than Taylor but ran from much further to get involved and did it under the refs nose, and then continued the verbals.