I have often seen characters throwing and puking blood when they are punched in the gut especially in Shounen animes like BNHA and Naruto Shippuden(well there are other animes I have seen this trope but I could think of these two anime for the time being). Why is it so common? Is it actually a trope? I have never seen someone throwing blood when punched in the gut IRL including boxing matches. Is it due to the fact that the punch is so strong that their organs gets damaged or collapsed leading to puking blood?
This trope is used to indicate significant physical damage to a character, through a force that would be at least significant to getting hit by a car.
Disclaimer, I am not a medical professional. The following based on prior received medical treatments and their explanations, and online articles.
In real life this can also occur, it is one of the symptom of severe hemorrhaging, which in it self is internal bleeding due to damaged blood vessel's.
Vomiting blood is considered a dangerous symptom which would require immediate medical attention.
A pretty good explanation on what Hemorrhaging is in near layman terms can be found on: medical news today