On February 19th, Profootballtalk reported that the Lions had cap charges of $98.1M, which would put the Lions at $17.9M under the projected cap of $116M. Two days later on February 21st, Adam Schefter of NFL.com reported that the Lions were only $6.8M under the cap. The Lions made no transactions on or around those days and the difference is a fairly significant $11.1M, so who's right and who's full of crap? The truth is, they are probably both right.
In order to understand why they might both be right, you need to understand the difference in how bonuses are calculated. Most player contracts, especially rookies, include incentive bonuses that are triggered when a player meets certain thresholds. They can be based on pretty much any statistic and include, but not limited to, playing time, passing yards, receptions, tackles, sacks, interception, offensive production, wins etc. These incentives can be based on either a single season or multiple seasons. The CBA classifies incentive bonuses into two types, likely to be earned bonuses (LTBE) and Non-likely to be earned bonuses (NLTBE).
LTBE Bonuses are bonuses that are, just like it says, likely to be earned. In the simplest terms, if a player reaches the threshold to trigger the incentive in the prior season, than it is deemed to be LTBE in the current season. Conversely, if he did not reach the threshold to trigger the incentive in the prior season, than it is deemed to be NLTBE in the current season. For rookies (i.e. Calvin Johnson), there are various charts within the CBA that specifies if and how much of an incentive bonus is to be deemed LTBE
Jon Kitna has thrown for more than 4,000 yards in each of the last two seasons. There could have been playing time or passing yards incentives that he triggered that resulted in bonus payments of a lot of money. Passing for 4,000 yards in a season is generally considered to be quite an accomplishment.
Calvin Johnson may not have had as good of a year as we had hoped for, but he didn't have a bad year from a rookie perspective. He could have triggered some incentives.
Ernie Sims has played in every game and has had a lot of tackles over the last couple of years. He could have triggered some incentives that were originally considered NLTBE.
Paris Lenon has also had a lot of tackles over the past couple of years, he could have triggered some bonuses.
A players contract and how it relates to the salary cap is very complex. LTBE and NLTBE incentives can greatly change a teams salary cap status and it can be a double edge sword. i.e. If a player reached an 2007 incentive threshold to trigger a previously classified NLTBE bonus, it will be reconciled at the end of the year and reduce the 2008 salary cap and if that same incentive is in the players contract for 2008, it will be considered a LTBE incentive for the current year and reduce the 2008 salary cap even more.
More than likely, both profootballtalk.com and Adam Schefter were correct with their reports of the Lions cap status, it's just that Adam Schefter's figure included the reconciliation of LTBE bonuses and NLTBE bonuses.