Sentinel's last function. What comes first, the attack or the reaction?

Question

Quick question of the order between enemy actions and friendly reactions.

Sentinel

• When a creature within your reach makes an attack against a target other than you (and that target doesn't have this feat), you can use your reaction to make a melee weapon attack against the attacking creature.

Does this happen before the enemy's attack goes through? So the player have a chance to kill the attacking creature before he attacks the players party member? Or does the enemy's attack connect first, giving the player an opportunity to attack the enemy?

Answer 1

After the triggering attack is resolved

From the DMG...

Various spells and features give a creature more reaction options, and sometimes the timing of a reaction can be difficult to adjudicate. Use this rule of thumb: follow whatever timing is specified in the reaction’s description. [...] If a reaction has no timing specified, or the timing is unclear, the reaction occurs after its trigger finishes

So, you have cases like the Shield spell where it says...

Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack

So in that case, it specifies that the Shield spell works on the attack that triggers it, so the Reaction to cast it must occur before the attack lands.

However, there is no such language in the Sentinel Feat--the timing is not specified, so the general rule of "reactions occur afters their trigger finishes" applies.