Opportunity Attacks With Spells

[Strill]

Opportunity Attacks allow you to perform one "Melee attack" (PHB p. 195). Notice it doesn't specify whether weapon or spell. Is there anything stopping me from using Shocking Grasp as my melee attack?

[Kryx]

Is there anything stopping me from using Shocking Grasp as my melee attack?
Shocking grasp is an action, not a reaction.

[Person_Man]

War Caster Feat gives you the ability you're looking for - when a hostile creature's movement provokes an Opportunity Attack from you, you can use your Reaction to cast a spell at that creature instead of an Opportunity Attack. The spell must have a casting time of an Action and must only target that creature.

FYI, the designers have Tweeted that it can't be combined with Polearm Mastery.

[themaque]

Not to mention there is a specific feat in order to pull this off, Martial Caster. So no you can't cast spells for an OA by standard.

[holygroundj]

Opportunity Attacks allow you to perform one "Melee attack" (PHB p. 195). Notice it doesn't specify whether weapon or spell. Is there anything stopping me from using Shocking Grasp as my melee attack?

Melee attacks are different than Melee spell attacks, in the same way that Ranged weapon attacks are different than melee weapon attacks.

[Strill]

Melee attacks are different than Melee spell attacks, in the same way that Ranged weapon attacks are different than melee weapon attacks.

No, Melee WEAPON attacks are different than Melee SPELL attacks. Melee Attack covers both Melee WEAPON attacks, and Melee SPELL attacks.

[Easy_Lee]

No, Melee WEAPON attacks are different than Melee SPELL attacks. Melee Attack covers both Melee WEAPON attacks, and Melee SPELL attacks.

True, but casting a spell is generally an action. Certain spells allow you to make a melee attack roll, but still require an action to cast. Hence, making a melee spell attack may be part of a spell, but is not the whole spell. As said, you need the warcaster feat to do what you're talking about, and it has limited crossover with other sources of opportunity attacks. One really has to read the fine print when it comes to OAs.