The following are several drafting theories some actually subscribed to by teams, others sometimes in name only:
Draft the best athlete: The most tried and true draft theory, though, it drives a lot of fans, particularly those who are more likely to be looking for a quick fix to distraction. It is also something of a misnomer; best athlete implies you are primarily taking a guy for his athletic ability - speed, vertical leap, weight-room strength etc. - when done correctly it really should read "best player available". Drafting the best player is also based on the notion that drafts are not primarily about fixing a weakness on the team for next year, but rather are part of a longer term building process.

Here's how BPA works, at least in theory. First, we give each veteran on a particular team a numerical grade which we will call their hypothetical player value (HPV) on a scale of ten. Then a team with a WR with HPV of 8 and an OG with a HPV of 6 and arrives at the draft and has a choice of two players: a WR with an HPV of 9 and an OG with an HPV of 8. Obviously by taking the OG the team would increase its value at that position by 2 points whereas by taking the WR their total HPV would rise only 1 point. In the short ternm the team would increase its total HPV by taking the OG. However, if a team did the same thing over a period of years, that is, took the player with a HPV of 8 at a position of need, but passed on a 9 at another position, at the end of a 5-year period, for example, that team would have a total HPV of 40 from the 5 picks, whereas the higher graded players would have added a total of 45, and everything else being equal a much better team. Given the incredible vagaries of pro football careers - injuries, FA defections, and the fact that all players develop differently and at different paces - this year's crisis at OG, for example, may have been solved by an undrafted FA no one counted on, while one at another position suffers a career ending knee injury - drafting the best player available simply maximizes your odds of having the best possible team over the long haul.

Of course, when a team makes its pick there is often not such a clear difference between players; in fact there may be several players with a similar ranking and that's when that team can focus on which of those players/positions will help that particular team the most.

The problem with BPA, however, is that, almost by definition, it does not do a good job of addressing problem areas. This can be be a major concern, particularly at positions like QB, left offensive tackle, RDE and CB where it is critical that a team have at least a competent player if they hope to be a serious contender. This is where free agency can, and should, come into play.

Shopping lists versus a truly positional draft: Most teams when drafting appear to take a kind of shopping list approach: a WR in the first round, LB in the second, OG in the third, DT in the fourth and so on. I am not sure, however, that this is necessarily very effective when a team is trying to upgrade a really weak position. In fact there is nothing that annoys me more on draft day when an announcer starts rambling on that "the Catfish have really upgraded their receiver core by taking WR Billy Bob Bumpkin from State U". I have always wondered how he knows; it could turn out the guy never signs, gets hurt on the first day of practise or actually couldn't catch a cold. The problem with just taking one player is that it is still all about probabilities, and probabilities far lower than we all realize. If that one player doesn't work out for whatever reason that team is ultimately no farther ahead. We believe that if a team really wants to work on a position they actually should consider using a good part of a draft to do it, again because of the generally low probabilities involved.

Team building rather than team fixing: Again, most fans - and indeed, most people in the media, not to mentiuon the myriad of mock drafters out there - when they look ahead to a draft, start with an assessment of the team's weaknesses and go from there. As such, they then tend to identify a top player at the weakest position as the 'player they would pick.' Most NFL coaches/management, particularly the good ones, however, often look more to proactively build something or a system rather than just look to fill shorter term holes. It may be to install a more diversified offense or develop an aggressive, attack oriented-defense or simply to get faster across the board; in order to do that, though, they often end up drafting players at positions which seem to be solid. And this phenomenon may be the biggest reason why predicting any draft is so difficult, because if often means having to get 'inside the head' of the respective coaches and GMs around the league.

Building from strength: We almost always talk about using the draft to fix weaknesses; this may not always be necessarily the most efficient way to build a team however. In a nutshell, the problem with this approach is that if a team brings a strong player into a weak unit, opponents can quickly neutralize the impact of that player by double-teaming or playing away from them. If on the other hand a team drafts to its strength, it is possible to create a super unit that make all other units on the team better simply because opponents have to invest so much in stopping the good unit that the weaker ones are allowed considerable liberties.

Building from strength: We almost always talk about using the draft to fix weaknesses; this may not always be necessarily the most efficient way to build a team however. In a nutshell, the problem with this approach is that if a team brings a strong player into a weak unit, opponents can quickly neutralize the impact of that player by double-teaming or playing away from them. If on the other hand a team drafts to its strength, it is possible to create a super unit that make all other units on the team better simply because opponents have to invest so much in stopping the good unit that the weaker ones are allowed considerable liberties.