Weak Strike On 28 Buffalo?

It can take some acquired skill to differentiate between a worn die and a weak strike, when most usually, they occur together. Same applies with worn dies in combination with worn coins.
Best to take the examples of uncirculated coins, so that the signs that suggest either worn dies or weak strikes are more easily identified and are not obliterated, and thus may be very hard to find on a worn coin.

A weak strike can be the result of a die pressure trial, where not enough pressure was used. The result is that lower points of the design are fully struck and the design detail is very sharp but the high points on the coin are not struck at all. That is an extreme case, but it illustrates the point. Such coins are usually re melted. More often, a weak strike that has been issued is more fully struck up, but the same principle applies.

A worn die can exhibit some of these features, but for a coin that has been struck using full die pressure, has the design features rounded something like a worn coin, but the fields retain a full radial mint lustre. Quite often with a badly worn die, there is some evidence of radial metal flow on the outside of any peripheral legend. There is evidence of tiny ridges that radiate outwards from the lettering towards the rim. This happens more with dies made in many decades ago, where the science of die hardening may have been less well understood. With worn dies it is usually the high points on the coin that show first evidence of die wear.

Both of the features of worn dies and weak strikes can be well hidden with worn coins.

Thus armed with this knowledge I will leave it to others to comment on the coin pictured. Perhaps I can learn a little more myself!

Too many tic marks on the coin.
I'd say it's been circulated.

I'm going to go with a well-worn die as evidenced by the flow lines - particularly on the reverse. Also too many nicks and dings to qualify as BU, in MY book, anyway. Note the north to south mark on the obverse that starts at about where the Indians mouth ends. If it's a clash mark, it's one I'm not familiar with. If it's not, then I'm not sure what it is....