Literally: *chou – *chou – emit – stop
Alternately: The sound of clashing swords; an argument as fierce as if it were a life-or-death sword fight.
Notes: 丁 has a number of meanings, such as a street or a ward of a town. It’s also used as a counter-word for a number of objects and as a signifier for the fourth item in an ordered series (along with 甲, 乙, and 丙) in the same way that the letter D might be in English. The character 々 doesn’t actually have a pronunciation of its own. It serves as a doubling mark to show that a kanji is repeated, so here 丁々 is identical to 丁丁. That said, none of that matters here: the character seems to be used purely phonetically in this phrase.
Similarly, although I give the most common meaning of the latter two characters, and 発止 seems like it might mean something that fits the content of the yojijukugo as stated… they too are purely onomatopoetic. It turns out that 発止 is a case of ateji, characters applied phonetically without regard to their meaning, and so hasshi is simply a sound that my dictionary describes as “with a loud clack.” So in the end, today’s four-character compound is probably best represented on a literal level as “clash clash clang.” Isn’t Japanese great?
Haven’t heard this compound before, thanks!