I've been noticing some interesting things about Rook's Hammerslam, mostly from the perspective of an opponent Regulus. 

Please keep in mind that I don't really play as Rook, so all you experts should add insight where you have it.

1.  Hammerslam seems to have a keyhole area of effect.  That is to say, there is a circular area of effect around the slam but it also appears to radiate out from the Rook in a line toward the enemy target for a significant distance. 

So if you run directly away from a slamming Rook you will most likely still take a hit, relative to how far you got before the hammer came down.  If you run to one side you will take little or no damage as long as you get out of the initial radius.  I have been half a lane away from a slam and still taken a direct-line hit, on Cataract.  I have been just to one side of the Rook when the slam came down and taken no damage. 

I haven't yet tested running through the Rook's legs to escape but this should work as well ^^ Edit: This has been shown to be the most effective method, per http://forums.demigodthegame.com/337806/#2037007

2.  Towers block slam effect completely, as long as you are completely silhouetted and the tower is targeted.  If you are playing Regulus and get behind a tower relative to the slam the tower will take all damage.  I haven't tested this with larger-profile DGs.  Edit: setup has to be perfect on this one.  If the tower is not placed directly between you and the slam you will still take damage.

What else?