Perhaps in the fanfic, Robin is captured by Harley Quinn. Batman arrives to save him. Harley Quinn taunts Batman, saying he's too late and that she's already turned Robin to her side. But Robin reveals it was all a ruse to get close to Harley and find out the Joker's next big plan. The scene could be filled with Harley's wild laughter and Batman's stoic determination.
In most cases, Batman would win. He has more experience, better combat skills, and a greater knowledge of various fighting techniques. Robin is still young and learning, although he is very talented.
One reason could be a difference in their methods. Robin might think Batman is too strict or old - fashioned in his approach to crime - fighting, and wants to do things his own way more freely. Maybe Robin has been influenced by new ideas or allies in Young Justice that Batman doesn't approve of.
Ra's al Ghul could also be a possible villain. He could use his influence on Robin, maybe through some sort of brainwashing or false promises. Ra's al Ghul might convince Robin that Batman's methods are holding him back from achieving true power or justice, and this could start the fight. Also, there's always the possibility of a new, original villain created specifically for the fanfiction. This villain could target their relationship and use mind - games to make Batman and Robin turn against each other.
The relationship can be complex. Batman could be seen as the stern mentor figure to Robin, while Harley Quinn is the wild card. Robin might be initially afraid of Harley but also a bit intrigued. For example, Harley could mock Robin for following Batman so blindly, which angers Batman. Robin might then stand up to Harley, showing his growth and loyalty to Batman.
The Penguin could be a great addition. His wacky and devious schemes always make for an interesting story. Also, Catwoman. Her complex relationship with Batman adds a layer of intrigue. And Oracle, who can provide valuable information and support from afar.
One interesting storyline could be Robin growing up and struggling to step out of Batman's shadow. He wants to prove himself as an independent hero while still respecting Batman's teachings.
In many Batman and Robin fanfictions where Robin is injured, it often leads to Batman becoming more determined to catch the villain. For example, in some stories, Robin gets injured during a fight with a new, powerful enemy in Gotham. Batman then uses his detective skills to track down the bad guy while also taking care of Robin. He might call in Alfred for help with Robin's injuries. This kind of situation shows the deep bond between Batman and Robin and how they rely on each other in tough times.
In my opinion, it's really hard to say who would win. Robin is young and agile, with a lot of new - style combat techniques. But Batman is experienced and has a vast array of gadgets and strategies. If the fight takes place in a more open area, Robin's agility might give him an edge in dodging Batman's attacks. However, Batman's wisdom and his ability to read his opponents could turn the tables. It really depends on the specific circumstances written in the fanfiction.