A wizard uses polymorph to become a Giant Ape. The ape takes damage, but the damage does not spill over into the wizard's hit points. Can this damage break concentration (if they fail the DC 10 or half-damage constitution saving throw)?
From concentration (PHB 203):
Whenever you take damage while you are concentrating on a spell, you must take a constitution saving throw to maintain your concentration.
Given that, while polymorphed, the wizard is the ape, damage taken by the ape counts under "whenever you take damage". Thus, the wizard must take a constitution save to maintain concentration (with the ape's constitution modifier).
Being polymorphed does not break concentration.