I made a fighter that got me thinking about relying on reaction too much is just not feasible without support.

WHich  leads me to; Quick Reflexes:  A feat that should be.

+1 to dexterity

gives one extra reaction per turn within limits.  Does not work with ranged attacks.  Thrown weapons are optional.  Works only within 5 feet.  If you have PAM, you could use one reaction at 10 feet, but the Quick Reflexes reaction would be  technically with the haft at 5 feet.  Regular reach weapons shouldn't find any difference.  See also echo knight. lol

DO you think this is balanced?

I wouldn't go into a second reaction. That is powerfull as hell, probably breaking a lot.

Maybe a second Attack of Opportunity within 5 ft., could be a bit too much still when combined with Sentinel.

An extra reaction per turn would be very powerful.  Because it's not just about attacks of opportunity.  

Okay, so, Quick Reflexes - suggested refinement 

Quick Reflexes - +1 to dexterity // an extra reaction, for attacks of opportunity within 5 feet only.

                       Limitations - does not work with sentinel. does not work with ranged weapons.  PAM enjoys regular reaction, with Quick Reflexes the attack of opportunity is represented by an attack with the haft of the weapon within 5 feet.  Regular melee weapons enjoy an extra attack of opportunity or can use a standard regular reaction for anything requiring a reaction and have an attack of opportunity available.

How about this, is it a better, more balanced?

Does multiple opponents provoking opportunity attacks come up a lot when you play? And even if so, why not just take Sentinel? Keeping one monster pinned to yourself must be more valuable than possibly injuring two monsters as they run around and eat your spellcaster?

So I took some time to think of what my response should be, it took awhile.  

It’s not a response to being like sentinel, or tanking, or anything along those lines.  It’s mechanically different flavor.  You could still wait for the conquest paladin or cavalier fighter to kick in to lock down an opponent.  It offers a dex bonus which does not bolster the mechanical aspects of cavalier and choosing the feat locks you out of sentinel.  Which is a thought.  Maybe it’s best used with two weapon fighting.  Or it allows someone loaded with many reaction choices a chance to use them and not give up an AOO.

Hopefully that’s well thought. 

Other reaction options are typically very powerful and can generally invalidate whatever attempted action triggered the reaction (see Shield and Counterspell in particular), but they come at a cost: you won't be able to do an opportunity attack. Any feat that allows you to cheese the action economy is probably overpowered in 5e.

(Given the discussions that's been about opportunity attacks and reactions in general on this fourm, I suspect that the way my groups have always played must be a well-spread house rule: reactions are taken and resolved in order of initiative. So A: someone's faster reaction can make it so that there is no longer anything for the next character to react to, and B: none of that "I'll wait and see what happens with another character's reaction first".)

A second AOO should be fine. Classes like Ranger and Artificer can get companions with essentially an additional AOO as a class feat, and their "feat" can even walk around, absorb damage and attack enemies. The same holds true for all casters with summoning spells.

It's strong, but a feat should be strong. It's not fun when one of only four choices you get to make in a characters life feels weak or insignificant.

Edit: I wouldn't even limit it with Sentinel and other feats. If a player combines those that's the equivalent to +4 to a primary attack or casting stat, which is *a lot* compared to "you might be able to attack two enemies a turn, if they behave stupid".

I'd honestly say a good way to balance this out too, would be to make it unusable if wearing heavy armor, and when wielding two handed weapons. That way a tanky fighter can stay a tank. 

The Cavalier capstone does something like this: " In combat, you get a special reaction that you can take once on every creature’s turn, except your turn. You can use this special reaction only to make an opportunity attack, and you can’t use it on the same turn that you take your normal reaction."

I'd word the feat exactly like this, but limiting it to one special reaction each round. This is good enough on its own that it would be worth a feat to many builds, so no +1 Dex. Might still be too strong at that. Reaction limits are the only thing holding back PAM/Sentinel builds from totally breaking many encounters and adding clauses like "this doesn't work with Sentinel" is just bad design and does not protect you from interactions with future released options.

I would say that it should be limited to a number of times per long rest.  Most of the feats which have a stat increase a have additional abilities which use up a resource (action or bonus action).  It it give an additional resource (like a spell being able to be cast without using a spell slot) have limited number of uses. Multiple reactions EVERY round of combat could just be breaking. I would have the number scale up as you level, maybe proficiency bonus times a day. 

I actually think this should be a core feature early on for monks. They have some extra reaction options, and even some associated with sub classes. 

A number of reactions equal to proficiency would be a nice way to make monks more unique. 

with the name I would have assumed it granted a bonus to initiative.

anything that plays with the action economy without a commensurate cost is dangerously broken.

As a rule of thumb when I play around with feats/spells/items that will have an effect on Actions I leave Bonus Actions and Reactions limited to one per round.

I'd go with a an additional reaction per long rest.

I'd go with a an additional reaction per long rest.