I have taken a look at kick and punt returns for TD's and here is what I have found.

I looked at NFL data for 2008, 2009, 2010, 2012 and 2013. The data is listed as follows, KR/PR TD's, league leader and total number of players who recorded a KR/PR for a TD.

Kick Returns

2008: 13 KR TD's, 2 KR TD's, 12 players
2009: 18 KR TD's, 3 KR TD's, 14 players
2010: 23 KR TD's, 3 KR TD's, 16 players
2012: 13 KR TD's, 2 KR TD's, 12 players
2013: 7 KR TD's, 2 KR TD's, 6 players

MFN-1
2013: 1 KR TD, 1 KR TD, 0 players - pre-KR changes?
2014: 0 KR TD's, 0 KR TD's, 1 player - pre-KR changes?
2015: 6 KR TD's, 2 KR TD's, 5 players - KR changes implemented?
2016: 12 KR TD's, 3 KR TD's, 6 players - thru 14 games

MFN-2
2013: 0 KR TD's, 0 KR TD's, 0 players - pre-KR changes?
2014: 1 KR TD, 1 KR TD, 1 player - pre-KR changes?
2015: 8 KR TD's, 2 KR TD's, 7 players - KR changes implemented?

The limited amount of data suggests that these numbers will increase, but may not get out of hand due to a limited number of kick returns. A few more seasons will be needed to better identify any problems.

Punt Returns

2008: 16 PR TD's, 3 PR TD's, 10 players
2009: 8 PR TD's, 2 PR TD's, 7 players
2010: 11 PR TD's, 3 PR TD's, 8 players
2012: 17 PR TD's, 2 PR TD's, 15 players
2013: 11 PR TD's, 2 PR TD's, 10 players

MFN-1
2013: 1 PR TD, 1 PR TD, 1 player
2014: 12 PR TD's, 2 PR TD's, 9 players
2015: 30 PR TD's, 6 PR TD's, 16 players
2016: 56 PR TD's, 7 PR TD's, 22 players - thru 14 games

MFN-2
2013: 10 PR TD's, 2 PR TD, 8 players
2014: 21 PR TD's, 3 PR TD's, 16 players
2015: 60 PR TD's, 9 PR TD's, 24 players

Punt returns for TD's appear to be broken. The 2015 data is almost equals the total NFL data for 5 seasons. Part of the problem may be how the punt return coverage is working. It seems that the defenders are getting too bunched up in the middle of the field which allows the punt returner to break to the outside and the endzone. The other issue is that more punts are being returned due to the lack of fair catches. I don't recall seeing any fair catches on a punt.

Thanks for the stats. Fair catches do get called, but right now the punter tends to outkick his coverage, so it doesn't happen very often. I do have on the TODO list to give punts more hang time which may solve this issue; but I'll make a note of your research and see if there are other issues that need to be investigated.

I was just going to post a question about punt trajectories after watching several punt returns for TD's. It looks like there are too many line drive punts at the moment which is causing quite a few issues.

Next up is a closer look at penalties.