Task: See the MAX values in D:D originating from variable sub data ("item") counts within "groups":

          A     B         C    D   ... X   
    1  Group A                 5      100
    2          Item1      3      
    3          Item2      5      
    4  Group B                 8 
    5          Item1      1      
    6          Item2      7      
    7          Item3      8      
    8          Item4      2      
    9  End                       

Solution "positive" (evaluate the range C:C until the last local entry in C:C): 

D1: =MAX(OFFSET(C2,,,MIN((1+$X$1-$X$1*(OFFSET(C2,,,$X$1,)=0))*ROW(INDIRECT("1:"&$X$1)))-1,))
must be entered as an array formula (Ctrl-Shift-Enter).

Solution "negative" (evaluate the range C:C before the first entry in A:A): 

D1: =MAX(OFFSET(C2,,,MATCH("*",OFFSET(A2,,,$X$1,),),))
No array formula. A9 must contain something.

Both: 
- Copy D1 manually to all "Group"-Headers, as to D4. 
- 100 items per group are preset in X1 which can be altered easily.