Grappled: A grappled creature is restrained by a creature,
trap, or effect. Grappled creatures cannot move and take a –4
penalty to Dexterity. A grappled creature takes a –2 penalty
on all attack rolls and combat maneuver checks, except those
made to grapple or escape a grapple. In addition, grappled
creatures
can take no action that requires two hands to
perform. A grappled character who attempts to cast a spell or
use a spell-like ability must make a concentration check (DC
10 + grappler’s CMB + spell level, see page 206), or lose the
spell. Grappled creatures cannot make attacks of opportunity.
A grappled creature cannot use Stealth to hide from
the creature grappling it, even if a special ability, such as
hide in plain sight, would normally allow it to do so. If
a grappled creature becomes invisible, through a spell or
other ability, it gains a +2 circumstance bonus on its CMD
to avoid being grappled, but receives no other benefit.

Grappled or Pinned: Casting a spell while you have the
grappled or pinned condition is difficult and requires a
concentration check (DC 10 + the grappler’s CMB + the
level of the spell you’re casting). Pinned creatures can
only cast spells that do not have somatic components.