This person's into sport in German city (6)
I believe the answer is:
weimar
'german city' is the definition.
(I've seen this before)
'this person's into sport' is the wordplay.
'this person's' becomes 'im' (this person means the crossword setter themselves).
'into' indicates putting letters inside.
'sport' becomes 'wear' (I've seen this before).
'im' placed into 'wear' is 'WEIMAR'.
'in' acts as a link.
(Other definitions for weimar that I've seen before include "German republic until 1933" , "German city; -- Republic" , "German city associated with Liszt and Goethe" , "German town associated with Goethe, Liszt and Schiller" , "13 [THIRD REICH] 's predecessor" .)