Yes, physical education can be included while calculating your best four for Delhi University but it has a disadvantage of 2.5%.
This means that 2.5% will be deducted from the total percentage of your best four subjects. This calculation of the best four is different for every course and very few colleges have a different method of selecting the best four and that is also limited to some special courses.
Apart from this, all the colleges have a similar procedure for the best four calculations. Delhi University releases an admission bulletin every year and you can consult it for better understanding.