Like in prior AC games, I just encountered a mission which was not much fun at all. Called
Chasing Hickey, your on-screen prompt is to do simply that. What you are not prompted to do is to tackle him; you just have to figure that one out on your own. If you simply chase him, he runs around New York endlessly in a convoluted circle. First I simply chased him but after the third go around town, I shot him with an arrow - the resulting desynchronization told me that was obviously not the solution. I next thought about tackling (which ended up being the solution), but because I never got tackling training I did not even know you could do it in the game (the key sequence is different than in prior games)
I had to finally do a search online as to what in the heck I am supposed to do, which in my opinion is a failure on the part of the programmers to cleanly develop a mission.
This is actually the first disappointment I have had while playing the game, and I have to say that this is worse than any other chase mission in prior AC games. :D
Here is an excellent video showing the solution:
Spoiler
As indicated in the description of the video, you need to tackle Hickey from the air, and on the PS3 the tackle sequence is evidently to hold R1 while twisting your thumb to press the "O" button
http://www.youtube.com/watch?v=YtNC3E1rHj8#ws (http://www.youtube.com/watch?v=YtNC3E1rHj8#ws)