I really don't want to resurect this old argument but…
Page 10 clearly lays out activations, which direcly effect the Overwatch situation disccused in the above topic. In the discused topic, the OP set up a situation in which a character begins their turn on the same path as a character on Overwatch, but then erroniously assumes that this character can simply choose to do nothing, which in TH they cannot.
All characters must activate, and when activated they must move or act, or some combo there of. So in this case the Overwatch character will at some point get a chance to attack the character that began the turn on their path, at least in the example dicused, it would take too long to lay out all the posibilties.
Here are the activation rules from page 10, as you can see there is no option to either not activate a character, or for an active character to do nothing.
4. Activate Characters
During this step, players alternate activating their characters. The player who has initiative goes first. If one player runs out of characters to activate (frequently because some of his characters have died, or are on overwatch), his opponent activates the rest of his characters one after the other. When his turn to activate a character comes, a player may choose to activate any character on his side who has not been activated yet and is not on overwatch. When activated, a character can move (see “Moving” on page 17) and take one action (see “Actions” on page 18). Taking an action is also known as acting.
During an activation, a character performs one of the following:
• Move and then act.
• Act and then move.
• Move, then act, then move some more.
• Move without taking an action.
• Act without moving.
Hope all that helps.