Throughout the series people have been shot or stabbed with small blood sprays.
A man's heart explodes after being stabbed by the Reverse-Flash. We see blood pooling from the wound.
In season 2 the flash is beaten until he bleeds and then has is back broken by an evil speedster
Barry is a forensics scientist for the Central City Police Department, so he works in CSI, and the crime scenes are mostly murders. However, the murders are usually committed by metahumans, so nothing gory is seen.
Season 6 is way darker than the previous seasons - Bloodwork creates a black zombie like army of people.
During the fight between Team Flash and Cicada, we see Nora getting hit by his dagger causing a brief and small blood spray. Her back is also broken
A man is killed with cards. Not bloody but disturbing
Flash first fight with Savitar is quite violent. It's not as violent as the first fight with Zoom though
"The Man In The Yellow Suit" is probably the most violent episode in the whole show. We see Harrison Wells getting violently beaten by Reverse-Flash. Some blood on his face
The episodes in prison in Season 4 are quite violent and leads to blood and gore
Season 1 has to be the most violent and bloody. There is way more bloody violence in this season than in the others
Season 3 is the darkest season but is not as violent as the first two. There is still brutal violence but most of it is bloodless
Season 4 is violent when it comes to the prison arc. Outside of that, it is the same level as season 3.
Season 5 is not that bloody but Cicada kills a lot of people in ways that could be considered gory. On the same level as Season 3 and 4 in terms of violence
Season 6 is darker on its first half. Bloodwork uses blood to create zombies. The second half is tame though
Season 7 is the tamest and barely contains violence. No blood at all.
A man who turned into a zombie explodes and a black liquid is seen instead of blood. Could be considered gory
In season 8, a woman has a stroke after facing an evil alien. She is seen with blood coming out her mouth. However, she is not dead
Several burned bodies are seen in season 8. Not too bad but it could be disturbing
Cicada and his niece have meta-human powers due to dark matter wounds on their chest and forehead, respectively.
Violence throughout is common, though not gory and actual blood is very rare. Some people are wounded (occasionally killed) due to powers of meta-humans. The Flash's first encounter with Zoom is violent, though most of the injuries inflicted are implied rather than seen. The only blood shown is on Barry's face.
