Shock Decanting (also known as splash-decanting) involves pouring a bottle of wine into a decanter while both the bottle and decanter are vertical, allowing the wine to hit the bottom of the decanter directly (as to splash off the bottom). It also involves the vigorous swirling (nearly shaking) of the decanter to add, mix oxygen into very young, tannic, closed, recently bottled red wines.
Normal decanting involves the pouring of an aged, fragile, quality bottle of red wine into the decanter at a slight angle, slowly and gently down the inside of the glass (thus removing the wine from any sediment or deposits that might be in the bottle) and then leaving it to settle, rest and breath on its own.

 

Most modern, young red wines will not contain or throw any sediment so the rate of the pour is not as important. Shock decanting for young, non-integrated wines - is simply vigorously agitating in order to introduce oxygen into the wine, by swirling the wine as much as possible inside the decanter - to create a frothy layer of small bubbles on the surface of the wine, releasing the defused carbon-dioxide (CO2) in the wine.
If you know the wine well or have been informed that the young red wine does not contain any sediment and is free from any suspended material - I encourage you try shocking decanter at your next dinner party. Depending upon the shape of your decanter - you can also pour the wine down the side of the decanter, but with more agitation and speed than normal.
I know that this sounds aggressive and is only suitable for a few wines. But you are seeing it more and more around the world - in top wine bars and restaurants. Where the wine staff are completely confident in their young red wines not having any sediment and that the increased agitation and the introduction of oxygen and the removal of the dissolved CO2 helps in opening up the wine - making it more approachable and enjoyable at a young age, stage in its natural development.
At home when I am familiar with the style and age of young red wines that I am opening - and I know that the wine would benefit from this technique. I will swirl the decanter vigorously like a blender without the lid on, making sure the wine does not splash out to lose any. At the ideal serving temperature for the wine in question, and only executing this technique for approximately 20-30 seconds. You will improve young, tight red wines which are closed and high in tannins; you will not be bruising or damaging the young well-made wine.
This technique is typically used on young red wines - but I have also used it on quality, well-made young, oak influenced Chardonnay’s that I take straight from the fridge and perform this process for approximately 10 seconds with great results. Though I find the most responsive style of wine to the technique with the best results are young, recently bottled quality Pinot Noir’s. Shock decanting can soften the youthful, assertive astringent characters in Pinot Noir's, and can open up the fruit flavours and also improve the palate feel and finish.

Please note: do not use this aggressive method for aged or fragile red wines - as you will only result in re-suspending any sediment or crust in the wine, plus making the wine cloudy, possibly losing subtle aromas, palate texture and making the wine appear tired and even unpleasant to drink.