My younger sister had joined the school hockey team and had a match after school one day. I had to wait for her this particular day as it would be dark by the time they had finished and showered, and our parents did not want her coming home on her own. I decided to watch the game whilst waiting for her. The sight of twenty two young girls running around in short skirts and knickers soon had my attention. There was one particular girl, a friend of my sister's, who was especially hot. She had her blond hair in a pony tail, and her tight fitting shirt meant her breasts bounced around for all to see. But it was her legs that had my attention. There were long and tanned and perfectly formed, and as she ran around her knickers would climb into her butt crack giving a fine view of her ass.
After the game my sister decided we would go straight home and she would shower there so I didn't have to hang around much longer. At home my sister showered and disappeared into her room. I need a to take a pee and went into the bathroom. Whilst peeing I noticed the lid of the hamper was askew and took a look inside once I'd finished. There on top sandwiched between her other clothing were my sister's gym knickers. Thinking back to the blond girl playing hockey, I took the knickers from the hamper and checked them out. They were thick and stretchy and just a bit damp too. I lifted them to my nose picturing my sister's friend having just removed them. They smelled of a mixture of sweat and pussy juice. My cock was rock hard now and I wrapped them around it and began jerking off, whilst thinking of the blond girl topless in just her gym knickers. The stretchy fabric caused just the right friction on my cock and I soon pumped my jism into the gusset of the knickers. I quickly wrapped them back up and beat a hasty retreat from the bathroom.