The feat Ranged Pin has as its benefit the following:
You can perform a ranged grapple attempt against an opponent by pinning a bit of its clothing to a nearby surface. The target must be within 5 feet of a wall, tree, or other surface in which a thrown weapon or projectile can be stuck and must be wearing some sort of clothing, armor, or other accoutrement. You must succeed on a ranged attack (not a ranged touch attack) and then win an opposed grapple check (your size modifier and the target’s size modifiers still apply). To break free, the victim must make a DC 15 Strength check or a DC 15 Escape Artist check as a standard action. (Complete Warrior 104)
The only other thing of interest is that the benefits of the feat Improved Grapple (PH 95-6) don't apply when using this feat. Neither errata nor FAQ nor online or Web Sage Advice column (that I've found, anyway) mentions the feat Ranged Pin. Opinions on the feat are mixed (see these threads from 2005 and 2012). I, however, just want to figure out how the feat works according to what it actually says.
That is, I am aware that—instead of having the feat use the grapple rules—the feat should probably simply render the opponent immobilized (Rules Compendium 35) until the opponent succeeds on the DC 15 Strength check or Escape Artist skill check, but that's not what the feat's benefit says it does.
Because I'd like to know how to (or if to) obey this feat's letter (not its spirit) before I house rule the feat for my campaign, a good answer walks through the steps of how this feat functions according to the rules as written.
As I can't determine how it couldn't be, it's okay if this walkthrough is a little silly (the attacker dealing its unarmed strike damage to the grappled opponent by shooting the opponent's cloak, the attacker able to move a thousand feet or more as a free action to enter the opponent's space to maintain the grapple, etc.).
Best Answer
Reading the rules in a strictly literal sense, I don't think it actually counts anything as a true grapple.
I think the only reason you make a 'grapple' check at all is to include all relevant size/skill factors. A Huge creature's arrows would basically be the size of a javelin to a small creature, so it stands to reason that bigger projectiles pin more successfully than smaller projectiles.
It doesn't specify that you or your opponent are considered to be in a grapple, nor does it specify that normal grapple damage applies (or constrict damage for that matter). It simply requires you to make a roll that uses all relevant bonuses for grappling in terms of size and strength.