And every year there are injuries on the defense and we watch James Ihedigbo/Sergio Brown/Tracy White/Malcolm Williams and so on lining up to try to stop an NFL offense. Drives me nuts, but BB is the greatest coach in football ...
I agree that Belichick has had problems acquiring safeties and keeping them healthy. Ihedigbo was, and probably still is, a valuable commodity as a special teamer and #4 safety. Sergio was an OK special teamer that Belichick hoped would be better. However, the problem was not that these guys were terrible starters. They were never intended to be close to getting lots of reps on defense. Belichick didn't have enough quality at the top 3 safety positions AND there were two injuries that forced guys like this to start.
SPECIAL TEAMS
In addition, one of the reasons that Belichick is one of the greatest coaches ever is his attitude toward special teams. Special teams are important to Belichick.
First the specialists are important. Kickers are paid serious money. There is often competition for punter and long snapper. Belichick uses starters at returner (Welker, Brown, Edelman, Hobbs, and others).
Starters are often key players on the special teams units. Some teams are not willing to risk top players in these roles. In addition, Belichick keeps 2-7 players who are on the squad because they are special team "starters", key player son the special teams. Yes, these players are usually emergency players at their positions, but the hope is they never get on the field as position players. The patriots have had this philosophy for many years. We have always had at least a couple of players who are on the team as "special teams only" players. These players are NOT on the bubble. Guys like Slater have special team roster positions, and are often much more important and likely to make the team that the bottom 7 players. The bottom seven often do include special teamers, who are sometimes cut and re-signed several times during the year. But make no mistake. Belichick will often carry many players who primary function is special teams.
Posters disagree with belichick's approach to special teams every season. Every season, posters say that we cannot "afford" to carry a LB or S who are primarily special teamers. And, every year, Belichick disagrees.
THE CORE AND BOTTOM TEN POSITIONS
The bottom ten positions can be used for lots of things: position backups in case of injury, developmental players and special teams. To me, 43 roster players are needed in a addition to addition special teamers. These 43, plus additional special teamers, will get almost all the reps.
OFFFENSE (19)
QB (2)
WR (4)
RB (3)
FB (1)
TE (2)
OL (7)
DEFENSE (19)
DL (7)
LB (5)
CB (4)
S (3)
SPECIAL TEAMS (5)
K (1)
P (1)
LS (1)
ST (2)
The highest priority in the bottom 10 positions for winning a game, or winning this season is likely to be special teams. Then, we often have developmental players (including rookies). Position backups, in addition to what is included in the 43, is often 3rd in priority.
To put in another way, if the 43 positions above were filled, I would first add our top draft choices and then look to special teams. For example, the top 43 likely doesn't include a kick returner.