Maybe this is used somewhere idk. Google is not my friend on this so far.
This is not just MFN related, but it could be used in RL too. Just by using simple tally marks on paper and recorded on a spreadsheet.

To me tackle made are not all created equal
A tackle made after an offensive player makes a first down = bad
A tackle made that prevents a first down = good
A tackle made for a loss(which is a stat) = really good

A tackle made after a first down is recorded as a "Save" as well as a "Tackle".
A Tackle for Loss counts as a "Tackle for Loss" and a "Tackle"
A Tackle on 3rd down that doesn't result in a first down counts as a "Tackle on 3rd down" and a "Tackle".

A "Tackle for Loss" is more important than a regular "Tackle" and is weighted more. And a "Tackle on 3rd down" is even more important and weighted the most.

Using the formula below you can get a ratio of tackles made before a first down is made. Thus gaging how well a defensive player is making plays.

Examples:
Player A
a) Tackles = 100
b) Tackle for Loss = 5(x2)
c) Tackles on 3rd down = 10(x3) (that were not first downs)
d) Saves = 25
e) Tackle Ratio = 82.1

Formula
e = 1 - d / (a+ (b*2) + (c*3))
82.1 = 1 - 25 / (100 + (10) + (30))

Player B
a) Tackles = 100
b) Tackles for Loss = 4
c) Tackles on 3rd down = 6
d) Saves = 37
e) Tackle Ratio = 70.6

Player C
a) Tackles = 90
b) Tackles for Loss = 7
c) Tackles on 3rd down = 17
d) Saves = 22
e) Tackle Ratio = 85.8

Note: Im not a math wiz by any stretch. I wrote down the formula the best way i could describe it.

Tackle for loss seems obvious that it's always a good play. However, the other two are not obvious, if you are talking about "good" or "bad" for the player.

Example:
A tackle made after the offensive player makes a first down is not always bad. If the defensive player got there as soon as possible and made the tackle immediately, it's not his fault the play resulted in a first down. He did all he could. Perhaps a poor defensive play call?

Conversely, if it's 3rd and 20 and the LB gets stiff-armed by the RB for 15 yards before finally bringing him down shy of the first down marker, I wouldn't call that a good play by the LB.

It's really hard to judge a player's performance strictly by looking at stats. Watching the game is really the only way to know for sure.

Yes I agree. Using this would not be beneficial on a play by play basis. What I was thinking in all this is to find a pattern throughout a players season or career.

The numbers should balance themselves out after enough data is supplied. So if a guy is late to the ball more often than not it's eventually going to show up as a low tackle ratio and vice versa. It would be position specific. Most safeties are going to have lower ratios than most LB's etc......

Overall, its a great point and idea/suggestion BC, it would provide a much better evaluation of a players defensive ability and contribution. Another thing that would help with player evaluation on defense is what the DBs allow on yards per catch. On offense, I would really like to get more stat results on the OL, especially run blocking results. All of that would significantly help in making player personnel decisions and who should start/sub. For some of us, maybe many, the player evaluation part of the game is one of the most interesting and fun things to do, so the more numbers/results we can get, the better!