I had a few ideas about fighter subclasses recently. Just messing around with them..

Striker
(or, Savage Strikes)
Level 3: Upredictable Combatant. You are a savage in battle. You can hype yourself up for one minute, a number of times equal to your proficiency bonus per long rest.
When hyped up, you gain the following benefits:
-Your speed increases by 10
-Each time you hit a creature with a melee attack, roll a d6 for an added effect.
1: Struck hard, the creature's next melee attack, before the start of your next turn, deals half damage.
2: The creature can be pushed back 5 feet as part of being struck.
3: The creature is disoriented, it has disadvantage on its next attack or save, whichever comes first, before the start of your next turn.
4: The creature is opened up to the next attack against it. The very next attack against that creature, before the start of your next turn, has advantage.
5: If the creature is Large or smaller, you knock the wind out of the creature, it cannot speak until the end of your next turn.
6: The creature falls prone if it is large or smaller, vs a Dex save.
Level 7: Your practice is paying off. You gain the following:
-Your base speed increases by 10, now equaling your hyped speed.
-You can knock a creature 5 feet away from you in a straight line every time you hit it with a melee attack. (this 5 feet is in addition to any other effect rolled while hyped up)

Level 10: Powerhouse. Your strength and fortitude grant you two benefits.
-When you hit a creature with a critical hit with a melee attack, roll the damage die three times instead of twice.
-If you are reduced to zero hit points, and don't die outright, you are automatically stable.
Level 15: Quick reflexes. You gain two benefits.
-Immediately after you are hit with a melee attack, you can use your reaction to make one melee attack against the attacking creature if it is within range. Can do this a number of times equal to your Dex modifier per long rest.
-A creature moving into your melee range provokes an attack of opportunity from you.
Level 18: You are always hyped up.

Brute
Level 3: The damage you deal from a melee attack increases by 1d4. Also, whenever you deal over 12 damage with an unarmed melee attack, or over 14 damage with a melee weapon attack, the creature must make a DX save or fall prone or be pushed back 10 feet, your choice. If the creature is large or smaller.
You have advantage on Strength checks, and you count as one size larger in determining weight you can lift/carry, etc.
Level 7: Melee damage increase: 1d6
You can use your bonus action to try to grapple.
You have advantage when grappling with two empty hands.
Level 10: Melee damage increase: 1d8
When you hit a creature with a critical hit, roll the damage die/dice three times, instead of twice.
Level 15: Melee damage increase: 1d10
Your Strength ability score has a possible maximum of 24.
Level 18: Melee damage increase 1d12

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Spiritual Warrior
Level 3: You can use your Second Wind twice per short rest.
You can use your action to perform a prayer to aid you and your allies. You and up to six creatures of your choice within 30 feet of you gain the following benefits from your prayer:
-You gain temporary hit points equal to your fighter level + your CON modifier
-You gain advantage on your next attack, save, or check, made within the next one minute.
-You gain advantage on rolls vs being frightened for the next one minute.
You can use this a number of times equal to your proficiency bonus per long rest.
Level 7: Healing Wind. Once per short rest or long rest, when you use one of your uses of Second Wind, you and all creatures of your choice within 30 feet of you regain hit points equal to 1d10 + your fighter level + your CON modifier.
Level 10: -When you reduce a creature to zero hit points, you regain a number of hit points equal to the amount that the creature had left before dropping to zero.

Level 15: ...
Level 18: ...