Its basically a blind min raise by the player that is UTG and it gives you the last action preflop, so lets say its dealer, SB, BB, you straddle now it folds around to dealer who calls and,SB calls,BB calls you have the option now to raise or check.
Some days I run so bad I flop a set and turn 2 pair.
It's a raise in the dark (before the cards are dealt), kind of like an additional blind & generally 2x the BB...anyone calling or raising after the straddler does so according to the amt of the straddle. When I've seen it done, in live limit games, it's usually the UTG position & it's used to create action.
Of all the things I've lost -- I miss my mind the most...
Wisdom is the principle thing; therefore get wisdom and with all thy getting, get understanding. (Proverbs 4:7)
Basically what's been said above - easiest way to picture it is as an optional third blind that UTG can elect to pay. Some games allow an overstraddle or restraddle too, which is an optional fourth blind that UTG+1 can elect to pay.
Each straddle should be double the size of the bet behind it so an UTG straddle should be 2BB and an UTG+1 restraddle should be 4BB.
As has been pointed out above too, the reason players (smart ones, at least) straddle is to encourage action in the game - not because they think it'll be advantageous to them to have last action preflop when they're out of position and the pot is artificially inflated.
This is why some players (Phil Laak or Phil Hellmuth on High Stakes Poker, for example) will only agree to straddle if the majority of other players are straddling as well. If that's the case, it means they pay the extra money when they're out of position but they're guaranteed that the pot will also be bigger when they're back in position again. Other players (degens like Eli Elezra, Tom Dwan, etc) are willing to do it whether the other players do or not and figure the image and other benefits are worth the cost.
TY All very much for your replies. I'm new to all this and just could not grasp what they were does on HSP straddling.
OzEx: TY for your further explination of "overstraddle and restraddle" as this was going to be my next Q ,lol. Now, OzEx can you explain "degen"? I suspect it is "degenrate", but maybe "De Genius's" too.