In plain words
Action begun through delusion, without regard for consequences, loss, harm, or one’s own capacity, is called tāmasa.
Word for word
Which action is begun from delusion without regarding the consequence, the loss, the harm and one's capacity, that is called tāmasa.
अनुबन्धं क्षयं हिंसामनपेक्ष्य च पौरुषम्मोहादारभ्यते कर्म यत् तत् तामसमुच्यते
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam· bhāṣya
अनुबन्धं पश्चाद्भावि यत् वस्तु सः अनुबन्धः उच्यते तं च अनुबन्धम् , क्षयं यस्मिन् कर्मणि क्रियमाणे शक्तिक्षयः अर्थक्षयो वा स्यात् तं क्षयम् , हिंसां प्राणिबाधां च ; अनपेक्ष्य च पौरुषं पुरुषकारम् ‘शक्नोमि इदं कर्म समापयितुम्’ इत्येवम् आत्मसामर्थ्यम् , इत्येतानि अनुबन्धादीनि अनपेक्ष्य पौरुषान्तानि मोहात् अविवेकतः आरभ्यते कर्म यत् , तत् तामसं तमोनिर्वृत्तम् उच्यते ॥ २५ ॥
In plain words
'Consequence' means whatever comes afterward — that is what 'consequence' means. 'Loss' means whatever depletion of strength or of wealth might occur in carrying out an action — that is 'loss'. 'Harm' means injury to living beings. And 'without regard to manly effort' — personal exertion, as in the thought 'I am able to complete this task' — means one's own sense of capability. So, disregarding all of these — consequence and the rest, right through to personal capability — action undertaken out of sheer delusion, without any discrimination, is called tamasic, born of tamas.
Close to the Sanskrit
'Consequence' — occurring afterward, whatever thing that is — that is called 'consequence'; that, and 'consequence'; 'loss' — in whichever action being performed a depletion of strength or a depletion of wealth would occur, that is 'loss'; 'harm' — injury to living beings; and, without regard to 'manly effort' — personal exertion, as in 'I am able to complete this task', thus — one's own capability; thus these, 'consequence' and the rest, ending with 'manly effort' — without regard to them, out of delusion, without discrimination, whatever action is undertaken, that is called tamasic, born of tamas.