In this passage, Jesus feeds the 5000, walks on water, heals people, and then the Pharisees gripe about him and his minions not washing their hands properly before eating.
From what I can see, there are two and a half responses to Jesus in all of these passages.
1). They wanted to force him to be king. Some people try to say that Jesus didn't really multiply the bread and fish. They say that when one little boy offered his lunch, the rest suddenly remembered that they had brought their lunchboxes and ate. No, no, no. This miracle is the only miracle other than the resurrection of Jesus that is in all four gospels. This was a huge miracle. This reminded the people of the manna in the desert and they also expected the Messiah to rescue them from Roman occupation and make Israel great again. So, they saw Jesus as at least the next Moses to lead them on another exodus and this was his sign. John 6 talks more about what went down than Mark does. The only thing is, he was already their king from eternity. And he didn't come only for them. And they needed an exodus from an occupation far more serious than the Romans. They needed salvation from hell and damnation. They needed to be saved from their sins. So, they had one extreme reaction where they approved of Jesus but wanted him to fulfill what they thought they needed rather than what he actually came to do.
1.5). Greater fear than any bad storm. After Jesus had graciously ministered to the masses, he still wanted some alone time after just having heard about his cousin, John the Baptist's death. He needed some grieving time. He send his minions across the lake without him. A big storm came and it was night. The disciples were freaking out. Then, here is Jesus walking on the water. This is the main way that Mark proves that Jesus is God. Only God could master the water and the waves that way and walk on them like it was just normal ground. When the hungry 5000 wanted to make him king, he showed his disciples that he was better than that, he was God the Son. And when he got to the boat, Mark uses his favorite word, "immediately," and the storm just stopped again. Once again, the disciples were more afraid after he calmed the storm than before.
2). The Pharisees completely reject and insult him. Most of their country sees Jesus as a man who is making changes. The Pharisees see someone not following the rules that they follow so well that they made rules around the rules. Apparently when Jesus fed all those people, he did not do the ceremonial washing that they think God the Father wanted because he wanted them to eat clean food. And if God wants them to eat clean food, then he must want them to wash elaborately, too. This is far more complicated than washing your hands in warm water for 20 seconds and then turning the faucet off with the paper towel before drying your hands. No, this is more like a whole bath.
Then again, God wanted clean hearts, not stupid rituals that he didn't actually set. And just like the first reaction, they went the other extreme where they disapproved of Jesus because he was not fulfilling what they thought they needed rather than what he actually came to do. Which is the right reaction? Neither extreme. We simply need to fear Jesus more than a storm the way the disciples did. So much will go right if we do so.