Was Crocodile stronger at Marineford? Or was he holding back in Alabasta?

 During the Alabasta arc, Crocodile displayed a level of power that was initially considered overwhelming by the Straw Hat Pirates. He possessed the Logia-type Devil Fruit called the Suna Suna no Mi (Sand-Sand Fruit), which granted him the ability to control and transform into sand. He had a reputation as a Shichibukai and controlled the desert kingdom of Alabasta from the shadows. His strength was showcased through his battles with Luffy and others. At Marineford, Crocodile was present as part of the war that took place at Marine Headquarters. While he did participate in the battle, he didn't display the same level of dominance as some other powerful characters present. This has led fans to speculate that he might not have been as strong as initially portrayed in Alabasta. It's important to note that power scaling and character abilities can be subject to interpretation and development by the author. Oda often keeps details deliberately open-ended to keep the story intriguing.

How did knights train to use their weapons and armor?

 Knights in the Middle Ages typically trained for years to become proficient in the use of their weapons and armor. Training usually began at a young age, often as early as 7 or 8 years old, and could last for several years.

Knights-in-training, or squires, were typically apprenticed to a more experienced knight, who would oversee their training and provide guidance. Squires were responsible for a variety of tasks, including maintaining the knight's armor and weapons, caring for the knight's horses, and assisting the knight in battle.

Squires also received formal training in the use of weapons, such as swords, lances, and shields. This training often took place in a specialized training area called a "tiltyard," where knights could practice their skills in simulated combat situations. Squires also learned about strategy, tactics, and battlefield protocol.

In addition to weapon training, knights also had to be physically fit and able to endure the demands of wearing heavy armor for long periods of time. To achieve this, they engaged in a variety of physical activities, such as horseback riding, hunting, and jousting.

Once a squire had completed his training and proven himself in battle, he could be knighted by a member of the nobility or by the king or queen. This ceremony, known as "dubbing," involved the squire being struck on the shoulder with a sword, and was followed by a celebration. Knights were expected to uphold a code of chivalry, which included virtues such as honor, courage, and loyalty.