Quantitative analysis research data and graphics by Adam Gabriel

All NFL teams take risks when it comes to adding free agents to the roster. The salary-cap space and cash are at risk every year when signing older players to free-agent contracts. The graphics and research below will demonstrate the type of quantitative analysis research vs. scouting (film evaluation) that front offices use in order to make decisions.

When looking at acquiring a free agent to fill key hot spots on the roster, there are three areas of major concern:

1. Character; make sure that character is good (non-criminal, locker-room guy, leadership qualities).

2. Play time; should have a high percentage of play time for the top free agents in the 90-100 percent area. This includes special teams as well.

3. Injury history; a major piece of the equation. If a player struggles to stay healthy, and has several injuries despite not being season ending, that is a major red flag when assessing free-agent possibilities.

Quantitative analysis data breaks down the odds of an aging veteran becoming injured or busting out when it comes to descending production. This information is used by personnel directors, general managers and contract negotiators who will figure out how to optimally structure the length of a deal, and determine the amount of guaranteed money versus incentives that will be offered.

The following research studied every defensive tackle that played at least one NFL season after age 32 during the free agency era (since 1993). Each player’s average production as measured by games played, games started, solo tackles, assists, sacks, sack yards, passes defended, fumbles forced, and fumbles recovered.

Then comparing how every defensive tackle performed in the seasons before and after age 32 and calculated the average percentage decline across all players. Visual aids were developed to show production regression over time in some of the more important categories.

As the charts demonstrate, teams can still squeeze starting level production from defensive tackles at age 33. However, at age 34, the numbers drop to the point where a player’s likely production is indicative of skill descending erosion and/or injury issues that dictate those tackles being only part-time starters and rotation contributors. In other words, they move from Red player (starters and heavy contributors) to Orange players (backup and special teams players that struggle to keep up with Red players). Obviously, negotiators would want to attempt to minimize guaranteed dollars and maximize incentives in these situations.

A recent example of the production split is Fred Robbins of the St. Louis Rams, who signed as an unrestricted free agent and promptly had a career year at age 33 in 2010, with career highs in sacks (6) and passes defended (8). In fact, Robbins recorded the highest passes defended total for a tackle over age 32 in the free agency era. To date, Robbins has not been as effective at age 34 in 2011, having tallied only one sack and defended one pass through 11 games.

(Note: Solo tackles were chosen as simple proxy for developing a probability forecast largely due to that category providing the largest sample size. The curve was not normally distributed. Also note that this study was completed before the start of the 2010 NFL season.)

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Click here to see the raw data.