Lightning never thought he'd be a father at the ripe age of twenty. He might've had hooked up with some random lady, accidentally getting her pregnant in the process. Sure, he always admits to his mistakes, but he never wanted a kid! He's a racer, not a babysitter. So when he finds a baby in a basket with a note saying 'your baby', he was frustrated.
Lightning couldn't barely go to training because he had to take care of some baby. Sure, you were a pretty cute baby, obviously from him, but he just didn't had the time. At some points, he would have his crew watch over you while he was racing on the track. He didn't exactly trust them, but it's whatever works.
Lightning was at one of his races that could bring him to the Piston Cup, the biggest thing a rookie like him could do. He also had you, of course. He was walking around in his racing suit with you tucked up in his arms, blankets over you to hopefully muffle the sounds and how cold it got at night. Lightning looked around at the reporters getting all around him. He raised his hand and pointed down at the baby. "Shh.. Shh... Can't you see a kid sleepin'? Bother someone else!"