C'è questa FAQ in merito se ti può interessare
When using a Ride skill check to claim cover from your mount, exactly when do you start claiming cover from your mount? When must you stop claiming cover from your mount? The skill description says you react instantly to claim cover, and it doesn’t take an action. Does that mean you can do so anytime, even when it’s not your turn? The skill description says you can’t attack or cast spells while claiming cover. Why is that significant if you can claim cover anytime without using an action?
You can make a Ride check to claim cover from your mount anytime, even when it’s not your turn. Make the check before your opponent makes his attack roll. If your check succeeds, you have cover against your opponent’s attacks. If several different opponents attack you during the same place in the initiative order, one Ride check determines if you have cover against all those attacks. If you’re attacked again, you must make another Ride check to claim cover again. You cannot claim cover while you’re casting a spell or making any kind of attack. So, for example, if you cast a spell while mounted, you can’t use your mount as cover against any attack of opportunity you might provoke. You also cannot claim cover from your mount while making a charge attack (not even during the movement portion of your charge).