Does a spell that normally requires concentration, but which is cast with and triggered by Contingency, still require concentration once it begins?
Part of the reason I ask is in comparison with a similar situation, in which a concentration spell cast into, and then triggered by, a Glyph of Warding lasts for full duration without concentration being required of anyone.
Best Answer
Yes, the contingent spell will still require concentration.
In 5e spells do only what they say they do. Contingency says nothing about modifying the effects of the contingent spell.
The only things contingency changes about the spell are that the effect is delayed until the condition is met and the target is changed to only target the person who cast contingency. Nothing about changing concentration or duration.
Compare this to Glyph of Warding (a spell that is similar in some ways to contingency) which specifically says:
Since there is no such wording in contingency, there is no reason to think that it does change anything to the contingent spell except what it is written in the spell effect already. Thus, the contingent spell will require concentration once it is triggered.
Official ruling - concentration is required
Jeremy Crawford agrees with the above in this clarification: