In plain words
Yet the turbulent senses can forcibly carry away the mind even of a discerning person who is striving, son of Kunti.
Word for word
For the turbulent senses forcibly carry off the mind even of a discerning person who strives, O son of Kuntī.
The commentators
Bhagavadgītābhāṣyam
सम्यग्दर्शनलक्षणप्रज्ञास्थैर्यं चिकीर्षता आदौ इन्द्रियाणि स्ववशे स्थापयितव्यानि, यस्मात्तदनवस्थापने दोषमाह —
यततः प्रयत्नं कुर्वतः हि यस्मात् कौन्तेय पुरुषस्य विपश्चितः मेधाविनः अपि इति व्यवहितेन सम्बन्धः । इन्द्रियाणि प्रमाथीनि प्रमथनशीलानि विषयाभिमुखं हि पुरुषं विक्षोभयन्ति आकुलीकुर्वन्ति, आकुलीकृत्य च हरन्ति प्रसभं प्रसह्य प्रकाशमेव पश्यतो विवेकविज्ञानयुक्तं मनः ॥ ६० ॥
In plain words
Anyone who wants the wisdom that is right seeing to stand firm in him must first bring the senses under his own control. And since that is so, the Lord now states what goes wrong when they are not brought under control —
"Of one striving" means: of one putting in real effort. "For" means: because. O son of Kuntī, of a man, of a discerning man — that is, a man of keen intelligence. As for the word "even," it belongs syntactically with a word further along in the line, not with the one next to it. The senses are pramāthin — churning is simply what they are — and they shake a man whose attention is already turned toward their objects; they throw him into disarray. And having thrown him into disarray, they carry off his mind, the mind already furnished with discrimination and clear knowledge. Prasabham: by overpowering him outright — and out in the open, while he stands there watching it go.
Close to the Sanskrit
By one wishing to bring about the steadiness of the wisdom whose defining mark is right seeing, at the outset the senses are to be placed under his own control; since, in the not-establishing of that, he states the fault —
Of one striving — that is, of one making effort; hi — that is, because; O Kaunteya, of a man, of a discerning one — that is, of an intelligent one; as for api, its syntactic connection is with a word placed at a distance. The senses, pramāthīni — that is, having agitation as their very nature — indeed shake the man who is facing toward sense-objects, they throw him into confusion; and having thrown him into confusion they carry off, prasabhaṃ — that is, by overpowering him, and openly at that, while he is looking on — the mind that is endowed with discrimination and clear knowledge.