Grappled by enemy vs forced movement spells and effects

Okay here's the scenario.  The Hobgoblin Warlord has grappled the halfling PC by the leg and starts running towards the cliffs edge where he plans to just throw her over into the ravine below.

Players argue that any kind of forced movement spell, Thorn whip, Eldritch Blast, Lightning lure ect.  Would automatically break the grapple by targeting the PC and either hitting her lower AC or having her choose to fail the save. 

I would argue that since the Warlord has her grappled that there should be some kind of opposed check on his end or they had to hit his higher AC.    His Athletics vs the spell save DC for example. 

It was a moot point during game because they only rolled 11 for the thorn whip and  a 12 for the eldritch blast.  But I'd like to have clarification it if comes up again 

Thanks in advance! 

Quote from BrianofKrypton1 >>

I would argue that since the Warlord has her grappled that there should be some kind of opposed check on his end or they had to hit his higher AC.    His Athletics vs the spell save DC for example. 

That is a reasonable opinion (and a reasonable ruling for a DM), I'd even say that it is one that many shares. But the rules has no such clause so your players are correct about the RAW side of this.

Have a look around, there are several threads about Grappling and forced movement and such that might help you deal with the situation.

Edit:
Fixed the tool tip

I created a topic recently about something like that, about grappling chains. Contested checks were removed in 2024. RAW (and probably RAI too), any kind of forced movement breaks the grapple.
Keep in mind that moving a target you are grappling normally costs your own movement speed. If movement happens and it's not your turn, you have no movement speed to spend to dragged your target along with you.

It's also a common misconception to picture a grappled target like their completely wrapped in the attacker's arms. But that would be the Restrained condition. Grappled is more like "the attacker is holding you by the sleeve, preventing you from moving away".