One of the most difficult aspects of playing poker successfully is learning how to deal with aggressive players. This is especially true for newer players who haven't acquired the experience to play against such players with the proper emotional detachment. What usually follows is an impatient or ill-timed counter-attack that is actually a well executed trap by the aggressor.
If you have a poker calculator, that kind of situation can be avoided by knowing exactly what the Aggression Factor (AF) of your opponent is, and what it means. If you use Holdem Indicator or Tournament Indicator the formula for aggression factor is AF = (Raise% + Bet %) / Call %. Now what this actually represents is aggression after the flop only so therefore also includes betting for the turn and river. Keep in mind that pre-flop raising has its own distinct category.
In essence the AF factor therefore shows the relationship between how many times a player bets and/or raises compared with how many times he simply calls. So let's say an opponent's AF is 2.0. Well that is on the aggressive side to be sure but what it represents (for example) is that the player raised 5 times, bet 6 times and called 6 times. So that's (5+6)/6=1.83 rounded up to 2.0. So as you can see by doing the math, this player prefers to lead the betting and probably only calls with odds and in position.
This player is probably experienced and knows what he is doing. There is nothing wrong with having an AF in this range and if the player is advancing his stack, while not making apparent errors, you can probably be assured he is dangerous and will be trying to trap you into handing over your stack. With a player like this, you need to take away the betting from him by betting first or re-raising. This player wants to play small ball, and will not like you re-raising, or betting out of position, taking the pot size out of his comfort zone.
Let's look at another player's AF just to compare. How about 11.5? Yes, you can get that high, and even higher. This player, let's call him WrecklessBob77, hardly ever just calls. If he is in a pot he is betting or raising the flop, no matter what. To get an AF this high WrecklessBob77 has bet 21 times and raised 13 times while only calling 3 times. That's (21+13)/3=11.33 rounded to 11.5. Chances are the Holdem Indicator Poker Calculator has profiled this individual as a gambler because the AF factor is weighed into the profiling, along with VPIP and WSD percentages.
With a gambler that has that high and AF, he is simply playing with too much aggression, especially if you see him in the lower limits. The fact that he is still around is probably the result of winning some big pots in marginal situations, excessive luck, and weak opponents. Those things never last nearly long enough, and this player WILL bet himself out of the game or tournament. The savvy players at the table will be drooling over his stack, simply waiting patiently to trap this maniac and bring it in. That's what you should do too while knowing your position on him every hand, but also realizing you need strong hands to play this guy, so as not to be another one of his bad beat victims.