French autorities say that banning away fans for this match had little to do with the safety for Ajax fans but rather the safety for the Marseille fans. "Agressive behavior is something that is seen a lot with Ajax ultras, who mostly operate under the name 'F-Side'. They are known as one of the most dangerous groups of Europe."
In 2009 things already went wrong between the two clubs when Marseille and Ajax faced eachother in the UEFA cup. Ajax fans went with a big group of fans to Marseille. Ajax fans were then attacked by Marseille fans with bricks, sticks and iron bars. Ajax fans then chased Marseille fans until police showed up. In the return in Amsterdam Ajax fans held up a banner saying "We had joy we had fun, we had L'om on the run".
Whether it's ajax or any other team it's always like that anyway, our fans complain every time about away fans restrictions but apart from AEK fans we can't have anyone come close to us without the most stupid behaviour coming out, doesn't even matter who started what, the reality is there's always a small group of fans who's too dumb to just go watch a game and behave. I don't have much love for the police and their awful organisation but I can somewhat understand why they'd rather avoid having visitors if they can.