When the Flash faces off against Danton Black, he's hit several times throughout the episode by Danton's fists. Yet, in many other episodes, when shot at, he can dodge bullets and react in time as if his reflexes are sped up. Why is it that he can dodge a bullet but not an obvious punch which is coming his way?
I can think of a few possibilities:
- Restraint: A speedster's fist should be able to hit with much more force than an ordinary human's. If Barry hit someone without nigh-invulnerability or a healing factor of some sort at super-speed, he could easily kill them. Therefore, in close combat, he holds back on using his full speed. When grabbing bullets out of the air, he has no concerns about causing damage to the bullets.
- Overwhelmed: In the Danton Black situation in particular, Flash was being hit by multiple assailants (even if they were all the same guy). With multiple hits coming from multiple directions (all in close proximity), it's hard to dodge. When handling bullets, they're usually all coming from roughly the same direction.
- Interaction: In order to talk to someone, he basically has to slow down to normal human speed. In at least some instances, this may have delayed or prevented his reacting with full speed.
- Speed of thought: There is evidence in the show that, while Barry can do things at super-speed, his brain is not necessarily running as fast as his body. In Season 2, we saw him using his speed to read books - but being unable to retain the contents well. If his brain was truly running as fast as his body, then he'd retain what he read as well as anyone would - because, to him, he's reading at normal speed - everyone else is just a lot slower. This may happen at a variable rate. When Barry sees a gun, he knows to expect bullets, and is prepared to shift into full speed mode to catch them; punches aren't necessarily as predictable.
And, of course, yeah, it's all plot device - if the story's more dramatic (or fits into 42 minutes better) if Barry gets the living snot beat out of him, then he'll get the living snot beat out of him.
The most basic answer i can think of is money. Not for him tho but for the creators of the show and the writer of the comics. In the show Barry can run so fast everything around him stops entirely or as its know in the show "Flashpoint". He could just stop all his enemy's as simple as stoping everything, picking them up and putting them in a containment cell. The only reason is that would not make it interesting at all. Tell me, would you want to see him win over and over like that. There is no thrill in that. So if i were to want to profit off of this I would make the fights more fun and challenging. Like when the bad guy get away Barry can just go into flashpoint and find them and bam bad guy caught, but that's boring. Another example is in avatar the last surrender. Aang can just go into the avatar state and kill Zuko in the begining to end all his problems but he doesn't because that would make no money. Hope this helps and to rephrase my answer. The show would not be watched and the comics would not be read because they are boring and that is not how to make money.