For this achievement you need to ride a titan and get 10 hits while riding it.
First place you can get this achievement during the campaign is when you're trying to get out the pumping area.
To ride the titan you need to batarang him when he is charging at you and give him a few hits till he is stunned on his knees. Press the action button and just walk up to enemies and he is swinging his arms himself and try to get 10 hits.