Of course, the first place the unit can rout is ADJACENT.
It must rout further, of course - interdiction is not mandatory, if there is a non OG it can move to from there.
The rule A 10.51 states that, if ADJACENT, it cannot move ADJACENT (but here it begins in the enemy's hex, which is different).
A 10.5 says it cannot remain in the ennemy's hex, thus understating it will first move ADJACENT... and rout further, as it cannot remain ADJACENT either...
Note that, as the Berserk unit is not "Good Order", the routing unit may also use Low Crawl to leave the ADJACENT Ground level without surrendering as per A 20.21, if it does not want to risk interdiction...
Now, rule specialists, don't burn me alive if I said something wrong! :wink: