Balance this baddie (minotaur battlerager)

[Ebon Rogue]

I'm designing a new creature with a theme in mind and some custom abilities to fit. An angry minotaur in spiked armor.
His abilities are a bit squirrely, but I'm thinking CR 3 or 4.



Monotaur Battlerager(patent pending)
Large Monstrocity
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Ac: 14(13 Natural, 1 Spiked Plates)
HP: 57 (6d10+24)
Stats: Str20(+5) / Dex8(-1) / Con18(+4) / Int10(0) / Wis7(-2) / Cha3(-4)
Skills: Athletics +9, Perception +2
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Serrated Armor. When the minotaur is hit by a melee attack within the minotaur's reach; the attacker takes 5 slashing damage.

Brutish Strength. The minotaur counts as being one size larger when used to calculate carrying capacity, shoving, and grappling.


Actions-----

Multiattack. The minotaur makes 2 attacks or uses Bull Rush

Thrash [Once per Round]. Melee Weapon Attack: +7 to hit, reach 5ft, all creatures in reach. Hit: 7 (1d4+5) slashing damage.

Horns. Melee Weapon Attack: +7 to hit, reach 5ft, one target. Hit 12 (2d6+5) piercing damage.

Unarmed. Melee Unarmed Attack: +7 to hit, reach 5ft, one target. Hit: 7 (1d4+5) bludgeoning damage

Bull Rush [Recharge 5-6]. Before moving, the Minotaur can charge in a straight line, up to twice its movement. If a creature is in the way and is large or smaller, make a grapple check when in range. On a success, the target take 12(2d6+5) piercing and is grappled by the horns. On a failure, the creature is moved to an adjacent tile(their choice) and takes 5 slashing damage. Once a creature has been grappled in this manner, the Minotaur automatically fails further grapple checks during this movement. The minotaur cannot use its Horn attack while a creature is grappled on the horns. If the Minotaur is stopped suddenly, the grappled creature takes 12(2d6+5) piercing damage and the Minotaur is stunned until the start of their next turn.
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I am hoping to have this type of enemy be a notable threat to a party, regardless of level. Something that should be trivial when the PCs understand it's tricks but, unless outplayed, can handle players like a bar bouncer if they dismiss the threat.

What do you guys think? Are the abilities to abusable for its rating? Or does it need some tuning in the stats?
I like the theme of a thrashing ball of spikes and horns, and would like to keep the abilities in some form, so I am looking for critique in how to balance this baddie(he said the title!).

[Seafarer]

Offensive CR: 14 (thrash hitting 2 creatures) + 12 (horn attack) + 10 (two creatures hitting the minotaur) = 36 damage per round. +7 to hit. The charge actually does less damage, so it isn't factored in. That gives us an offensive CR of 5.

Defensive CR: 57 HP, AC 14. That's defensive CR 1/2.

Total CR: (5 + 0.5)/2 = 2.75, rounded to CR 3.

Other comments: Why is your Athletics skill only +4? It should be +5 from ability score alone. Also, your Thrash ability as written is one attack roll against multiple targets; is that intentional?

[Ebon Rogue]

Other comments: Why is your Athletics skill only +4? It should be +5 from ability score alone. Also, your Thrash ability as written is one attack roll against multiple targets; is that intentional?

It's a mistype, its supposed to be +4 from proficiency and expertise(well, the monster equivalent). +9 total. Its what makes Bull Rush useful(and screws with CR). He is supposed to man handle players like they're dolls using grapple and shove. Carbot's Zerg Infestor (https://www.youtube.com/watch?v=IxOm86GB9nQ) comes to mind with the level of grapple control :D

I didn't know how to word thrash, its a melee attack that targets all creatures in reach(so 8 possible in an extreme circumstance). I couldn't find an equivalent "attack" within the DMG. I would work it under the assumption that it would make one attack and the attack roll vs everyone's AC to determine if it hits individually. I might make just make it a DEX Save at DC13 for 1/2 damage if the wording can't be done correctly.



Also, should of posted this in Homebrew, mb.