Because he refused to accept Shawcross' apology for the tackle. Which, to be fair, is a toolish thing to do since the injury was clearly not intended and Shawcross was obviously pretty upset about it.
Agree about the tackle but you can understand why Ramsey had the hump
![Wink ;) ;)](/styles/default/xenforo/vbSmilies/Normal/wink.gif)
The way some Arsenal fans have made Shawcross out to be some sort of monster on the back of that tackle and the way Stoke fans are now booing Ramsey, is stupid though.