import pandas as pd

d = ({
    'ST_A' : [0,0,0,0,0,1,1,1,1],
    'PG_A' : [0,0,0,1,1,1,2,2,2],
    'ST_B' : [0,1,1,1,1,1,1,1,1],
    'PG_B' : [0,0,0,0,0,0,0,1,1],
    'Area' : ['','','X','','X','','','','X'],
     })

df = pd.DataFrame(data = d)

ST_A  PG_A  ST_B  PG_B Area
0     0     0     0     0
1     0     0     1     0
2     0     0     1     0    X
3     0     1     1     0
4     0     1     1     0    X
5     1     1     1     0
6     1     2     1     0
7     1     2     1     1
8     1     2     1     1    X

cols = ['ST_A','PG_A','ST_B','PG_B']
df[cols] = df[cols].diff()
df = df.fillna(0.)
df = df.loc[(df[cols] == 1).any(axis=1)]

ST_A  PG_A  ST_B  PG_B Area
1     0     0     1     0
3     0     1     1     0
7     1     2     1     1

indexes=np.where(df['Area']=='X')[0].tolist()
indexes2=list(map((1).__add__,np.where(df[df.columns[:-1]].sum(axis=1) < df[df.columns[:-1]].shift(-1).sum(axis=1).sort_index())[0].tolist()))
l=[]
for i in indexes:
   if min(indexes2,key=lambda x: abs(x-i)) in l:
      l.append(min(indexes2,key=lambda x: abs(x-i))-2)
   else:
      l.append(min(indexes2,key=lambda x: abs(x-i)))
print(df.iloc[l].sort_index())

Area  PG_A  PG_B  ST_A  ST_B
1          0     0     0     1
3          1     0     0     1
7          2     1     1     1