IMMOBILIZED
When you can’t move, you can’t use your Dexterity bonus (if any) to Armor Class, and you can be sneak attacked even when you’re not flanked or caught flat-footed.
Any of these conditions keep you from using your Dexterity bonus to Armor Class: grappled, held, helpless, incapacitated, pinned, or stunned. Immobility is one time when the uncanny dodge ability doesn’t foil a sneak attack (see the section on uncanny dodge).
Grappling is worth a special note. When you’re grappling, you lose your Dexterity bonus to Armor Class (if any) against any foe that you are not grappling, and that’s true no matter who started the grapple -- you’re just as vulnerable if you initiate a grapple as you are when a foe grapples you. You retain your Dexterity bonus to Armor Class, however, against a foe you are grappling. So, if someone grabs you, you can’t sneak attack that foe, but your buddies could.
When you’re climbing (ascending or descending a vertical surface or a slope too steep to walk up) you cannot use your Dexterity bonus to Armor Class, which makes you vulnerable to sneak attacks (even if you have uncanny dodge). Being entangled impedes your movement and reduces your effective Dexterity score, but it does not make you vulnerable to sneak attacks.
